May Day protests mobilize a growing outcry against Trump.

“We’re here to support our workers and our union,” said Jena Olsen, 63, who has been a flight attendant for 39 years, at a large rally in Chicago’s Union Park. But demonstrators said they were also angry about the “threat to democracy” posed by President Trump.

“I think the two coexist,” Ms. Olsen said, “and this huge turnout shows that.”

A separate effort, which organizers billed as a National Law Day of Action, brought legal professionals to the Supreme Court in Washington and federal courthouses across the country on Thursday to push for judicial independence and oppose efforts to intimidate law firms.

The lawyers demonstrating at the Supreme Court reaffirmed their oaths to serve with integrity and to protect the rule of law — principles that do not appear to interest Mr. Trump, said Fabiola Gretzinger, 28. “He thinks he’s above it,” she said.

Police closed streets for the crowds in major cities including New York, Los Angeles, Philadelphia and Washington. But protesters also rallied in small communities that voted overwhelmingly for President Trump, including places like Norman, Okla., Sauk City, Wis., and Hendersonville, N.C. Groups held signs in front of municipal buildings and public schools, and some demonstrators wore red to indicate support for public education.

A rally in downtown Los Angeles began early on Thursday and focused largely on migrant rights. Jose Servín, 31, an organizer for a statewide coalition of advocacy groups who helped set up for the rally, held a sign that read, “Come for one of us, come for all of us.”

Mr. Servin immigrated to the United States as a child, he said. “I found a place here where I can succeed, where I can thrive, where I can plant roots — I’m a father now — and I’m going to fight like hell to protect that,” he said.

The protests — more than 1,000 were expected across the country — were spearheaded to coincide with traditional May Day labor rallies by 50501, a loose coalition of grass-roots activist groups, as well as by labor, nonprofit and civil rights organizations. May Day commemorates the struggle for an eight-hour workday, won by labor organizers in 1886 only after clashes in Chicago resulted in the deadly Haymarket Riot.

Labor groups made up a significant portion of demonstrators at the rally in Chicago on Thursday, though pro-Palestinian activists and anti-Trump demonstrators swelled their ranks, and many saw their concerns as overlapping.

“He’s tearing apart our Constitution,” said Bill Hincks, 40, a union official from the Chicago suburb of Oak Forest, who faulted Mr. Trump for firing officials at agencies that regulate workplace safety, including at the National Labor Relations Board.

The Trump administration has sought to quell dissent in corporate America, universities, government agencies and the news media. But in recent weeks, demonstrations opposing the president’s agenda, as well as resistance from some of the institutions targeted by Mr. Trump, have increased in size and frequency.

Gov. JB Pritzker of Illinois, a Democrat who first ran for office in 2018 because of his revulsion to Mr. Trump’s first term, called for an even larger outcry during a speech on Sunday in New Hampshire.

“It’s time to fight everywhere, and all at once,” he said.

Katie Benner contributed from Washington.

On Wednesday, the Trump administration sued Hawaii first, seeking to block the lawsuit before it could even be filed.

The Justice Department also filed a nearly identical suit against Michigan, where Attorney General Dana Nessel has retained three private law firms to pursue climate change litigation but has not yet sued. The main thrust of the administration’s argument is that the federal government should determine national energy policy, not individual states.

Legal experts said it was highly unusual to sue to block other lawsuits that have yet to be filed.

Nine Democratic-led states have already sued fossil fuel companies over climate change, along with dozens of municipalities around the country, including Honolulu and Maui. The oil industry and its allies have tried to get those cases thrown out by making similar arguments to the ones put forth in the Justice Department filings this week.

The lawsuits filed this week in Hawaii and Michigan cite President Trump’s April 8 executive order, “Protecting American Energy From State Overreach,” which argued that state policies inhibiting the energy industry weaken national security and drive up costs for Americans. It also said that the other lawsuits already filed by states over climate change could result in “crippling” damages to oil companies being sued.

Michael Gerrard, director of the Sabin Center for Climate Change Law at Columbia University, said it was “at least highly unusual” to try to preemptively block lawsuits. “The usual procedure would be to move to intervene in existing lawsuits,” he said. “I’ve never heard of a situation where a lawsuit is filed to seek an injunction against somebody else filing a lawsuit.”

He predicted that such a legal strategy would not fare well. “Procedurally, it’s wacky,” he said.

Both suits, filed in federal courts in Hawaii and Michigan, named the state, its governor and attorney general. The offices of Mr. Green and the Hawaii attorney general, Anne Lopez, did not immediately respond to requests for comment.

Ms. Nessel called the lawsuit “at best frivolous and arguably sanctionable.” She said Mr. Trump had “made clear he will answer any and every beck and call from his Big Oil campaign donors” and called the lawsuits “perhaps the most surprising debasement of both the White House and D.O.J. yet.”

The legal and political battles have been escalating rapidly around the roughly three dozen cases brought by state and local governments against energy companies.

In January, the Supreme Court denied a request by the defendants in Honolulu, including Sunoco, Exxon Mobil and Chevron, to review a Hawaii Supreme Court decision allowing the case to proceed. In March, the justices declined to review an action brought by Republican-governed states against Democratic states that had sued oil companies.

Those efforts could have knocked down the entire batch of cases, which supporters call “climate deception” cases, because many center on the argument that oil companies concealed their knowledge about climate risks. Their detractors argue that they are an unlawful attempt to dictate energy policy at the expense of consumers.

Separately on Thursday, the Justice Department sued New York and Vermont in federal courts in those states over new “climate superfund” laws that seek to recoup costs for damage from storms and floods.

In a news release, Attorney General Pamela Bondi said, “These burdensome and ideologically motivated laws and lawsuits threaten American energy independence and our country’s economic and national security.”

The New York law put the amount sought at $75 billion. The Vermont law set out a lengthy process to determine the amounts it would pursue.

In its lawsuits against New York and Vermont, the Justice Department is seeking a declaration that the two states’ laws are unconstitutional and to block their enforcement. The two measures were already facing legal challenges from Republican-led states and industry groups.

The appeal to Chinese nationals reflects the priority John Ratcliffe, the C.I.A. director, has placed on increasing the agency’s intelligence collection on China. In a note to C.I.A. officers last month, Mr. Ratcliffe said China was atop the agency’s priority list.

“No adversary in the history of our nation has presented a more formidable challenge or a more capable strategic competitor than the Chinese Communist Party,” Mr. Ratcliffe wrote. “It is intent on dominating the world economically, militarily and technologically, and it is aggressively trying to outcompete America in every corner of the globe.”

Mr. Ratcliffe has also told members of Congress that the C.I.A. needs to rebuild its human intelligence collection efforts: case officers recruiting Chinese officials to steal secrets from the Chinese government.

Last year the C.I.A. released instructions in Mandarin about how people in China could safely use the dark web to contact the agency. The text-only instructional video was viewed 900,000 times. While the Chinese internet is locked down and censored, American officials believe that more sophisticated Chinese officials know how to work around those controls.

A U.S. official said the agency would not have made the most recent, highly produced, videos if the instructional video had not worked.

In a statement Thursday, Mr. Ratcliffe said the new videos were aimed at “recruiting Chinese officials to steal secrets.” “Our agency must continue responding to this threat with urgency, creativity, and grit, and these videos are just one of the ways we are doing this,” Mr. Ratcliffe said.

One of the new videos released Thursday shows a midlevel official struggling in his daily life as he attends to a more senior official, who is living a comfortable life of fancy meals, clothes and cars. “The party raised us to believe that our dedication to the path they lead us on would bring prosperity to us all,” the midlevel official narrates. “But the gains of our collective efforts are indulged by a select few. So, I must forge my own path.”

The final scene shows the midlevel official using a mobile phone to securely contact the C.I.A.

The other video plays on fears that the Chinese government is arresting and ousting senior officials without explanation.

“I see my position rise within the party as those above me are cast aside,” the video’s narration says. “But now I realize that my fate is just as precarious.”

The video shows the senior official avoiding Chinese government agents closing in on him. As he fears for his career, the senior official says he must find ways to protect his family. The video closes again with images of the official contacting the C.I.A.

“My purpose remains the same,” the video concludes. “Only my path has changed. No matter what my fate may bring, my family will know a good life.”

The 36-page ruling by Judge Rodriguez, a President Trump appointee, amounted to a philosophical rejection of the White House’s attempts to transpose the Alien Enemies Act, which was passed in 1798 as the nascent United States was threatened by war with France, into the context of modern-day immigration policy.

The Supreme Court has already said that any Venezuelans the White House wants to expel under Mr. Trump’s proclamation invoking the act must be given a chance to challenge their removal. But Judge Rodriguez’s ruling went further, saying that the White House had improperly stretched the meaning of the law, which is supposed to be used only against members of a hostile foreign nation in times of declared war or during a military invasion.

While Judge Rodriguez’s decision applied only to Venezuelan immigrants in the Southern District of Texas — which includes cities like Houston, Brownsville and Laredo — it could have an effect, if not a binding one, on some of the other cases involving the administration’s use of the Alien Enemies Act.

“The court concludes that as a matter of law, the executive branch cannot rely on the A.E.A., based on the proclamation, to detain the named petitioners and the certified class, or to remove them from the country,” Judge Rodriguez wrote.

He also found that the “plain ordinary meaning” of the act’s language, like “invasion” and “predatory incursion,” referred to an attack by “military forces” and did not line up with Mr. Trump’s claims about the activities of Tren de Aragua, a Venezuelan street gang, in a proclamation invoking the Alien Enemies Act.

The American Civil Liberties Union has so far filed at least eight lawsuits challenging the statute in Texas, New York, Colorado, Pennsylvania, Nevada, Washington and Georgia. Federal judges in six of those cases have issued provisional orders stopping the administration from using it to expel Venezuelans accused of belonging to Tren de Aragua to a prison in El Salvador.

Lee Gelernt, the A.C.L.U.’s lead lawyer in the cases, praised the ruling by Judge Rodriguez.

“This decision correctly recognized that the president cannot simply declare there’s an invasion and invoke a wartime authority during peacetime,” Mr. Gelernt said. “As the court recognized, Congress never intended this law to be used in this manner.”

The White House did not immediately respond to a message seeking comment.

Early in his decision, Judge Rodriguez rebuffed an argument by the Justice Department that he lacked the authority to even consider the White House’s use of the act, which has only been used three times in U.S. history: during the War of 1812 and during World Wars I and II.

Department lawyers have consistently maintained that even judges have no power to intrude on the president’s decisions in matters of foreign policy. And while Judge Rodriguez acknowledged that the Alien Enemies Act gives the president “broad powers,” he also said that judges still have the ability to determine whether presidents were using the law correctly.

“The court retains the authority to construe the A.E.A.’s terms and determine whether the announced basis for the proclamation properly invokes the statute,” he wrote.

Notably, however, the judge disclaimed authority to examine the truth of Mr. Trump’s underlying statements, including his assertion that Tren de Aragua is controlled by the Venezuelan government — a claim that U.S. intelligence agencies disagree with. The judge said that because such assessments were for the political branches to determine, he had to accept Mr. Trump’s findings at face value.

Still, Judge Rodriguez determined that Mr. Trump’s use of the law did not comport with the definitions of key terms in the act. He rejected, for example, the president’s claims that the arrival of large numbers of Tren de Aragua members to the United States could be construed as an invasion or what the act refers to as a “predatory incursion.”

“In the significant majority of the records, the use of ‘invasion’ and ‘predatory incursion’ referred to an attack by military forces,” Judge Rodriguez wrote, adding that those terms “involve an organized, armed force entering the United States to engage in conduct destructive of property and human life in a specific geographical area.”

Judge Rodriguez, 56, was the first Latino Mr. Trump nominated to the federal bench during his first term. He was a partner at the powerful Houston law firm Baker Botts, and for years worked in Latin America with International Justice Mission, an evangelical Christian group that fights human trafficking.

Judge Rodriguez’s order applies to a class of plaintiffs. That means that unless Thursday’s ruling is overturned on appeal, the government will be barred from detaining or removing anyone from his district using Mr. Trump’s invocation of the Alien Enemies Act.

While the A.C.L.U. has largely been successful in stopping the Trump administration from continuing to deport people under the act, it has not yet been able to bring back to the United States the first batch of nearly 140 Venezuelans who were removed under the law to El Salvador on March 15.

Those men remain in the custody of jailers at a notorious prison known as the Terrorism Confinement Center, or CECOT.

Last week, lawyers for the American Civil Liberties Union asked Judge James E. Boasberg, the chief judge in Federal District Court in Washington, to order the administration to return those men to U.S. soil so they could get the due process they would have received if they had not been rushed out of the country.

In seeking to persuade Judge Boasberg that he had the authority to tell the White House to bring the men back, the lawyers cited a Supreme Court ruling in the case of another immigrant deported to El Salvador, Kilmar Armando Abrego Garcia.

In that decision, the justices said the White House needed to “facilitate” the release from Salvadoran custody of Mr. Abrego Garcia, who Trump officials have repeatedly admitted was wrongly sent to El Salvador on the same group of three planes that transported the Venezuelan men.

The Justice Department was expected by the end of Thursday to file court papers opposing the A.C.L.U.’s request to bring the men back from El Salvador.

But just as some of the mental health programs are starting, the Education Department canceled the funding this week and informed grant recipients that they would have to reapply for the money because of potential violations of federal civil rights law.

The department did not specify a civil rights law or provide the grant recipients with any evidence of violations, according to the notice reviewed by The New York Times.

An Education Department spokeswoman confirmed that the grants had been discontinued because of a particular focus on increasing the diversity of psychologists, counselors and other mental health workers.

“Under the deeply flawed priorities of the Biden administration, grant recipients used the funding to implement race-based actions like recruiting quotas in ways that have nothing to do with mental health and could hurt the very students the grants are supposed to help,” said Madi Biedermann, the department’s deputy assistant secretary for communications. “We owe it to American families to ensure that taxpayer dollars are supporting evidence-based practices that are truly focused on improving students’ mental health.”

Ms. Biedermann declined to provide applications that the department viewed as discriminatory, citing privacy laws. Instead, she offered examples of specific provisions pulled from lengthy applications.

A provision in one application set a “diversity goal” of hiring eight nonwhite counselors out of a total of 24. A line in an additional application included training for mental health professionals that included helping counselors “recognize and challenge systemic injustices, antiracism and the pervasiveness of white supremacy to ethically support diverse communities.”

Another highlighted the importance of handling “racial stress and trauma” of students. One applicant’s training included understanding “the influences of racism and white privilege in education practice.”

The grant cancellations were reported earlier by The Associated Press.

Senator Christopher S. Murphy, a Connecticut Democrat who helped negotiate the legislation, said it was illegal for any president to halt funding approved by Congress and called on Republican supporters to stand up for the law. Three Republican senators, John Cornyn of Texas, Susan Collins of Maine and Thom Tillis of North Carolina, who wrote a column in support of the law three years ago, did not return calls seeking comment.

“I’m raw about this because I sat in the room for a long time negotiating a really delicate compromise on a really tough issue,” Mr. Murphy said in an interview. “What’s the point of being in Congress and writing laws if the president can just ignore them? So, I’m angry that my Republican partners are not out there raising objections to what the president is doing.”

Christopher Rufo, the conservative activist who has spearheaded the assault on critical race theory and diversity, equity and inclusion programs, posted screenshots on social media this week of some grant applications, which he said was proof that the program was “being used to advance left-wing racialism and discrimination.”

“No more slush fund for activists under the guise of mental health,” Mr. Rufo wrote.

But Mary Wall, a former deputy assistant secretary for education involved in setting up the process to solicit bids for the program under the Biden administration, said it was a “gross overstep” to equate mental health services with the radicalization of children.

The application process favored programs that reflected the communities they served, she said. Programs aimed at training mental health professionals for predominantly minority communities, for example, received extra consideration if they could show how the training would be aimed at professionals with similar backgrounds. Ms. Wall said this was “a common-sense practice” with proven results.

“One of the first questions after every single school shooting is whether the student had access to mental health support and services,” Ms. Wall said. “It is no stretch to say that taking away this support introduces the risk of harm to school communities and students.”

Mr. Garland’s policy was a major shift after two decades in which the Justice Department had become increasingly aggressive in prosecuting leaks as crimes, a tactic that was vanishingly rare in the 20th century but became routine in the 21st under administrations of both parties.

Mr. Garland changed the policy after the revelation in 2021 that the Justice Department, under Attorney General William P. Barr, had secretly pursued email records of reporters at The New York Times, The Washington Post and CNN during President Trump’s first term. At the time, Mr. Garland said that a flat ban on such tactics was necessary to “allow journalists to perform the crucial work of informing the public without fear of legal consequences.”

Ms. Bondi had foreshadowed that she intended to roll back Mr. Garland’s rule in a memo last week, decrying leaks. The Justice Department, Ms. Bondi wrote, “will not tolerate unauthorized disclosures that undermine President Trump’s policies, victimize government agencies, and cause harm to the American people.”

A document detailing the new regulation says it is meant to address “growing concerns about federal government employees intentionally disseminating confidential, privileged, or otherwise protected information to the media or the purpose of undermining executive agencies’ legal obligations and policies.”

Media lawyers on Thursday morning were poring over the document, but at first glance, the language of the regulation appeared in many respects to revert to the department’s guidelines before Mr. Garland’s changes, which had been issued by the Obama administration.

Generally, the rules require Ms. Bondi herself to sign off before investigators may use compulsory legal processes to seek information about news-gathering activities, like orders to phone companies to provide logs of communications or subpoenas for reporters’ notes or testimony.

The new regulation contains a version of a pre-Garland guardrail that states investigators should exhaust other potential means of obtaining the evidence they are seeking before going after reporters’ information. “The government should have made all reasonable attempts to obtain the information, communications records, or business records from alternative sources,” the regulation reads.

The regulation also says that investigators generally should first pursue negotiations with the affected member of the news media before requiring a phone company to turn over that journalist’s records, but it allows Ms. Bondi to make an exception if she decides such talks would “pose a substantial threat to the integrity of the investigation, risk grave harm to national security, or present an imminent risk of death or serious bodily harm.”

Mr. Kennedy is one of the nation’s leading vaccine skeptics, and he has been vocal about his disdain for mRNA technology, which was used to develop coronavirus vaccines during the first Trump administration. He once wrote on social media that “mRNA jabs don’t stop infection, don’t block transmission, don’t block mutants, don’t last, don’t work at all.”

Mr. Kennedy’s activism in recent years included petitioning the Food and Drug Administration to pull the Covid vaccine off the market in 2021, during a deadly phase of the pandemic. He also urged the F.D.A. not to authorize Covid shots for children. Mr. Kennedy has also maintained that there could be a link between vaccines and autism, and hired a discredited researcher into his agency whose work aligns with that view.

Since becoming health secretary in February, Mr. Kennedy has made few high-profile pronouncements on vaccine policy, with the exception of his tepid endorsement of the measles shots in response to the outbreak in Texas that has killed two children and one adult. But he and the Trump administration have waded into the issue in other ways, by ordering a study on vaccines and autism and delaying approval of another Covid vaccine.

Mr. Kennedy’s announcements on Thursday represent an extraordinary use of his power as secretary to make decisions ordinarily left to career scientists at the F.D.A. The moves follow his recent instructions that parents of newborns considering vaccination should “do your own research.”

Mr. Kennedy has said he intends to restore trust in the vaccine approval process, but Dr. Jesse Goodman, a former F.D.A. official and an infectious diseases doctor at Georgetown University, said the changes could erode trust.

“Questions never bother me,” Dr. Goodman said, “but it’s really worrisome when it seems like they’re so ubiquitous and so constant that they sow a huge amount of doubt — not just about the one thing, but about everything.”

Most immediately, Mr. Kennedy’s move could affect the next round of Covid booster shots, expected to become available in the fall. Both flu shots and Covid boosters have been authorized without extensive human trials to target new strains of the virus as it has evolved.

Mr. Kennedy says the new policy will not affect flu shots, but the future of Covid boosters is now in doubt. Andrew Nixon, the department spokesman, said that because so many people have been infected and now have immunity to Covid, new studies are required.

“As we’ve said before, trials from four years ago conducted in people without natural immunity no longer suffice,” he said. “A four-year-old trial is also not a blank check for new vaccines each year without clinical trial data, unlike the flu shot, which has been tried and tested for more than 80 years. The public deserves transparency and gold-standard science — especially with evolving products.”

Mr. Kennedy’s plan for the placebo studies, first reported by The Washington Post, also raises ethical questions. It is considered unethical to deprive even a small group of patients of effective vaccines against deadly pathogens. In the case of Covid-19, new clinical studies could hold up authorization for boosters, which would leave the entire U.S. population vulnerable.

Dr. Ofer Levy, a Harvard vaccine researcher and a member of the F.D.A.’s vaccine advisory committee, said that would be “unacceptable,” and that officials must “thread the needle” to be sure the studies are done in a way that do not leave older and immunocompromised people unprotected from Covid.

“Tens of thousands of people can die without protection against Covid,” said Dr. Levy, who co-founded a company working on an opioid vaccine.

The Centers for Disease Control and Prevention reported about 23,000 deaths from Covid since September, with as many as 1,000 a week that month and in January. Still, uptake of the Covid boosters has been low: About 23 percent of adults got the updated Covid shot released in the fall, according to the C.D.C.

One C.D.C. study of the Covid boosters used in 2023 and 2024 found that they averted about 68,000 hospital stays, and were most effective in people who were older than 65 or immunocompromised.

The health secretary’s familiarity with vaccine trials stems at least in part from his reviews of decades-old vaccine approvals, including for the polio vaccine and the measles, mumps and rubella vaccine. Mr. Kennedy has also helped represent plaintiffs in lawsuits against manufacturers.

He and the organization he founded and once led, Children’s Health Defense, have repeatedly complained that vaccines are not tested against placebos in clinical trials when they are being developed. The organization has cited polio, hepatitis and meningitis vaccines as examples, all of which were introduced decades ago.

“Every other medicine is tested against a placebo,” Mr. Kennedy said on a podcast in January 2020, in claiming that vaccines are exempt from that requirement.

That, however, is not entirely correct. Cancer drugs and other medications authorized under the F.D.A.’s accelerated approval program are regularly authorized after trials without a placebo. And new vaccines, including the vaccines for Covid, were tested against placebos — inert substances, such as a saline injection, or in some cases against vaccines for other diseases.

“We’ve required placebo-controlled trials for most vaccines, and sometimes it’s an inert placebo, and sometimes it’s an irrelevant vaccine,” said Dr. Peter Marks, who was the Food and Drug Administration’s top vaccine official until he was forced out in March. “The claim that we have not done randomized trials for pediatric vaccines aside from Covid is not correct.”

Mr. Kennedy has also raised concerns in the past about testing a vaccine against what many scientists consider a reasonable placebo: the same formula, but without the immune-activating agents. Mr. Kennedy has noted that the practice leaves uncertainty about whether ingredients in the formula could cause harm.

In addition to the new placebo requirement, Mr. Kennedy also announced a National Institutes of Health initiative to turbocharge the development of new inoculations for Covid, bird flu and seasonal flu — an effort that appears to be part of a broader assault on mRNA technology, or “platform.”

Since they were developed, Mr. Kennedy issued numerous social media posts about the mRNA shots, including one positing that the F.D.A.’s assessment of the Moderna shot for children in 2022 was “dishonest, and evidence that the public health establishment has abandoned science, logic, reason, rationality, empathy, health and medicine.”

The N.I.H. under the Trump administration has subjected studies related to the mRNA platform to strict scrutiny. Bills restricting the use of mRNA vaccines have popped up in Republican-controlled state legislatures, including in Texas, Idaho and Kentucky.

The F.D.A. is also holding up approvals of a Covid vaccine that is not based on mRNA technology.

The agency was expected to issue a decision on April 1 regarding whether to issue a full approval of the more traditional protein-based Novavax Covid shot, which had been used under emergency authorization. The F.D.A. delayed the decision, though, asking the company to conduct additional research.

“I’m curious if this administration actually intends to just obliterate the Covid vaccine,” said Richard Hughes, a lawyer with the law firm Epstein Becker Green who represents some vaccine makers.

Pfizer and Moderna, makers of the mRNA Covid shots, did not respond to questions about whether updated shots will be available in the fall in the United States.

A spokesman for Moderna said the company has run clinical trials for its booster shots before and after their launch. During an earnings call Thursday, president Stephen Hoge said the company tests its vaccines against placebos. A policy change had not been communicated to the company directly, he said, but “we will absolutely engage constructively and making sure we understand what those needs are and that we fulfill them.”

The new N.I.H. initiative, meanwhile, would develop a “next-generation vaccine platform” that would be “fully government-owned,” the department said. The N.I.H. helped develop the mRNA platform, and the vaccine maker Moderna paid the government hundreds of millions of dollars to license a key patent on the vaccine, though the company and the government later got into a dispute over the patent rights.

The mRNA platform relies on small bits of genetic code, which generated online rumors and conspiracy theories that it was being used to insert microchips into vaccine recipients. The new platform, by contrast, would rely on a more traditional method of vaccine development, which uses inactivated viruses to provoke an immune response.

The department said the new platform would be developed using beta-Propilactone, which is already a component in vaccine development but is considered a hazardous substance by the Environmental Protection Agency when people are exposed to it in large doses.

“From his time in uniform on the battlefield, in Congress and, as my National Security Advisor, Mike Waltz has worked hard to put our Nation’s Interests first,” Mr. Trump wrote in a post on social media. “I know he will do the same in his new role.”

Mr. Waltz had been on thin ice as national security adviser for months, but his position became more precarious after revelations that he organized a group chat on the commercial messaging app Signal to discuss a sensitive military operation in Yemen and accidentally included a journalist in the conversation. His job was saved at the time in part because Mr. Trump, aides said, did not want to be seen as giving in to the news media by firing Mr. Waltz.

By then, most of Mr. Trump’s advisers had already viewed him as too hawkish to work for a president who campaigned as a skeptic of American intervention abroad and was eager to reach a nuclear deal with Iran and normalize relations with Russia.

Mr. Waltz’s deputy, Alex Wong, who worked on North Korea issues in Mr. Trump’s first term and who is considered a more moderate Republican with substantial national security experience, is also expected to be removed, according to a senior administration official with knowledge of the situation. The official and others spoke on the condition of anonymity to describe the internal discussions.

Mr. Rubio now has a lengthy list of job titles. He holds the position of secretary of state and national security adviser, something that no other official has done simultaneously since Henry Kissinger held both titles under the Nixon and Ford administrations. Mr. Rubio has also been serving as the acting head of both the gutted U.S.A.I.D. and the National Archives.

The Kissinger experiment has not been considered a success by most historians. The national security adviser is supposed to help adjudicate among competing arguments inside a national security establishment, and thus must often resolve differences among the State Department, the Pentagon and the intelligence agencies, among others. Mr. Kissinger was ultimately removed from the post of national security adviser and replaced with Brent Scowcroft.

But Mr. Trump is not running a second administration that has much of a true historical parallel.

One person with knowledge of the discussions said Mr. Rubio had indicated some time ago that he would be willing to serve for roughly six months if he were asked to do so.

Mr. Rubio ran against Mr. Trump in 2016, but they have developed a close working relationship in recent months, according to several top administration officials. Mr. Waltz is being provided a soft landing and praise as he departs the current role, while filling the U.N. ambassador spot left open when Mr. Trump abruptly pulled his nomination of Representative Elise Stefanik, Republican from New York.

A person with knowledge of the events said that Mr. Waltz was not seen as an easy fit ideologically for the president or the rest of his team. Discussions about replacing him have been occurring in private for weeks, but they intensified after the leaked Signal chat.

Mr. Waltz did not join Mr. Trump for a trip to Michigan marking his first 100 days in office as had been planned, although the person with knowledge of the events said that was because he was handling a foreign policy matter.

The decision to remove Mr. Waltz was so abrupt that many on Mr. Trump’s staff only learned of it Thursday morning, as it was being discussed among senior officials in the White House. By midmorning, top aides were told it was true that he would be removed, and to await Mr. Trump’s statement, according to the person with knowledge of the events.

Tammy Bruce, the State Department spokeswoman, learned of Mr. Rubio’s new role during a briefing with reporters, after Mr. Trump posted about it.

The selection of the next national security adviser will be a critical one, at a moment when the president’s top national security and foreign policy aides have differed sharply on how to handle three of America’s most potent adversaries: China, Russia and Iran.

Mr. Trump is making the change just two weeks before his first major trip abroad, to Saudi Arabia and other Arab capitals in the Middle East, and in the midst of tense negotiations with Moscow and Tehran. Mr. Waltz joined him in Rome a week ago, for the funeral of Pope Francis, and was in the background of the meeting in St. Peter’s Basilica with Volodymyr Zelensky, the president of Ukraine.

Mr. Waltz, a veteran who had favored a muscular U.S. foreign policy for many years before Mr. Trump’s rise, had struggled to prove his bona fides to his base.

He also barely had time to organize a staff, much less tackle the hardest issues facing the president. Ordinarily a new national security adviser writes the administration’s national security strategy, often a yearlong process that involves hashing out differences among government agencies and cabinet members.

On some major issues — including how to engage China on its ambitions in the Indo-Pacific, its fast-growing nuclear program, its sophisticated cyberattacks on the United States and its allies and its effort to reunite Taiwan with the mainland — the administration has barely gotten started.

But Mr. Waltz was also seen by the senior team closest to Mr. Trump as struggling to show he could manage the role while managing his relationship with the president. One senior official said he had at various points been seen as seeking to minimize Susie Wiles, the White House chief of staff and the adviser in the building who is closest to Mr. Trump.

On Thursday morning, just as word of his ouster was beginning to circulate in national security circles in Washington, Mr. Waltz appeared on Fox News. A person with direct knowledge of the situation said that Mr. Waltz was aware that something was going to happen before he went on.

Mr. Waltz, who never made the public evolution toward Mr. Trump’s foreign policy views that Mr. Rubio did over the past several years, has been arguing internally for sharp sanctions against Russia if it fails to agree to a cease-fire with Ukraine. Mr. Waltz made that suggestion as an option for handling Russia as recently as Monday at a meeting with the president and senior members of his national security team, according to a person with knowledge of what took place.

So far, Mr. Trump, who has repeatedly voiced skepticism of the long-running United States efforts helping to defend Ukraine, has been reluctant to take anything but symbolic action against Russia, though at times he has threatened on social media to impose sanctions and tariffs.

And Mr. Waltz has been under siege by external allies of Mr. Trump for weeks, including the far-right activist Laura Loomer. Ms. Loomer had prompted the president to have Mr. Waltz fire several National Security Council staff members for what she perceived as disloyalty to Mr. Trump, after an extraordinary Oval Office meeting. Ms. Loomer had also aggressively targeted Mr. Wong.

Mr. Trump had been loath to fire anyone from cabinet-level positions since he took office a second time, seeking to avoid the headlines about the chaos that engulfed his first term.

Mr. Trump fired his first national security adviser, Michael T. Flynn, within four weeks of his inauguration in 2017, saying he did so because Mr. Flynn, a retired lieutenant general, had lied to Vice President Mike Pence about talks he held with the Russian ambassador.

Mr. Trump ran through four national security advisers in his first term. One of them, John R. Bolton, wrote a memoir about his time working for the president that was deeply revealing, and embarrassing, to Mr. Trump.

In his second term, Mr. Trump has appeared interested in avoiding not only headlines about the chaos, but also alienating people who could become vocal critics.

Labor groups made up a significant portion of the rally in Chicago on Thursday, though pro-Palestinian activists and anti-Trump demonstrators swelled the ranks. The event was one of more than 1,000 protests in cities across the country, organized by a loose coalition of grass-roots activist groups known as 50501, as well as labor, nonprofit and civil rights organizations, to coincide with traditional May Day labor rallies.

A separate effort, billed as a National Law Day of Action, brought legal professionals to the Supreme Court and other locations to push for judicial independence and oppose the Trump administration’s efforts to weaponize the Justice Department and intimidate law firms.

Large crowds were anticipated in New York, Los Angeles, and Washington, where police closed streets. The area around City Hall in Philadelphia will also be shut down for an evening event where Senator Bernie Sanders, independent of Vermont, is slated to speak.

A rally in downtown Los Angeles focused largely on migrant rights. Jose Servín, 31, held a sign that read, “Come for one of us, come for all of us.” Mr. Servin is an organizer representing a statewide coalition of advocacy groups marching on Thursday.

“I found a place here where I can succeed, where I can thrive, where I can plant roots,” said Mr. Servín, who immigrated as a child. “And I’m going to fight like hell to protect that.”

Organizers in small towns say they are also expecting dozens, if not hundreds, of participants at protests in front of municipal buildings and public schools, with some wearing red to indicate support for public education. In Norman, Okla., and Sauk City, Wis., demonstrators planned to stand on bridges and display signs for motorists.

The Trump administration has engaged in efforts to quell dissent in corporate America, the civil service, universities and the media. But in recent weeks, demonstrations opposing Mr. Trump’s agenda, governing style and expansion of executive power have increased in size and frequency.

Town halls have become unruly and combative, pushing many Republican lawmakers to avoid facing voters altogether. And collective efforts by universities, nonprofit groups, unions and even some law firms have slowly started to build momentum against the administration.

Gov. JB Pritzker of Illinois, a Democrat who first ran for office in 2018 because of his revulsion to Mr. Trump’s first term, called for an even larger outcry during a speech on Sunday in New Hampshire.

“It’s time to fight everywhere and all at once,” he said. “Never before in my life have I called for mass protests, for mobilization, for disruption. But I am now.”

ICE said the operation was one of the biggest in a single state in the agency’s history.

“This is a model that’s going to be implemented throughout the country, allowing us to have a force multiplier that can come to the table,” said Madison D. Sheahan, the deputy director of ICE.

ICE officials said the operation targeted people with deportation orders and those with criminal histories. More than 60 percent of those picked up had either an arrest or a conviction, the agency said.

Since January, the Trump administration has expanded the number of agreements it has with the local authorities to help with immigration enforcement. The Florida agencies involved in the six-day operation had signed such agreements as well. ICE has signed more than 400 agreements with local law enforcement since January, the agency said.

Those agreements are part of the 287(g) program, which allows local law enforcement to collaborate with federal officials on immigration enforcement.

Typically, in recent years, that meant local law enforcement helped ICE with migrants already detained in their local lockup. But lately the agency has given power to local law enforcement to make immigration arrests.

Austin Kocher, a research professor at Syracuse University who analyzes immigration data, said that ICE has signed over 200 agreements allowing local officers to make arrests since the beginning of the administration. ICE has long had the ability to pair up with the local authorities on operations, but the ability of local law enforcement to make arrests on their own would help the agency the most, he said.

Scott Shuchart, a former senior ICE official in the Biden administration, said the expansion of local law enforcement assisting ICE could help free up officers to handle other key parts of the deportation process, like working with representatives of other countries to obtain travel documents for removal and preparing flights. If it happens elsewhere, he said, it could expand ICE’s ability to ramp up deportations.

Mr. Shuchart warned that the effort would be limited to areas willing to help ICE.

“It’s going to be very regional, though,” he said. “I expect most big cities outside Texas and Florida are going to want to keep their local tax revenue for things only local police can do and leave the immigration work to the feds.”

The program has faced pushback in the past. The American Civil Liberties Union wrote letters this year to various local law enforcement officials advising them not to participate in such programs.

“They have a history of harming public safety, imposing serious financial burdens on localities and leading to civil rights violations,” one letter read.

In 2010, the inspector general at the Department of Homeland Security said that ICE and local law enforcement “were not operating in compliance with the terms of the agreements.”

By 2012, the Obama administration stopped signing agreements with local police that allowed them to help with immigration arrests and focused mostly on getting officers to help transfer migrants who were already in local lockups.