If he regains power, Donald Trump wants not only to revive some of the immigration policies criticized as draconian during his presidency, but expand and toughen them.

Former President Donald J. Trump is planning an extreme expansion of his first-term crackdown on immigration if he returns to power in 2025 — including preparing to round up undocumented people already in the United States on a vast scale and detain them in sprawling camps while they wait to be expelled.

The plans would sharply restrict both legal and illegal immigration in a multitude of ways.

Mr. Trump wants to revive his first-term border policies, including banning entry by people from certain Muslim-majority nations and reimposing a Covid 19-era policy of refusing asylum claims — though this time he would base that refusal on assertions that migrants carry other infectious diseases like tuberculosis.

He plans to scour the country for unauthorized immigrants and deport people by the millions per year.

To help speed mass deportations, Mr. Trump is preparing an enormous expansion of a form of removal that does not require due process hearings. To help Immigration and Customs Enforcement carry out sweeping raids, he plans to reassign other federal agents and deputize local police officers and National Guard soldiers voluntarily contributed by Republican-run states.

To ease the strain on ICE detention facilities, Mr. Trump wants to build huge camps to detain people while their cases are processed and they await deportation flights. And to get around any refusal by Congress to appropriate the necessary funds, Mr. Trump would redirect money in the military budget, as he did in his first term to spend more on a border wall than Congress had authorized.

In a public reference to his plans, Mr. Trump told a crowd in Iowa in September: “Following the Eisenhower model, we will carry out the largest domestic deportation operation in American history.” The reference was to a 1954 campaign to round up and expel Mexican immigrants that was named for an ethnic slur — “Operation Wetback.”

The constellation of Mr. Trump’s 2025 plans amounts to an assault on immigration on a scale unseen in modern American history. Millions of undocumented immigrants would be barred from the country or uprooted from it years or even decades after settling here.

Such a scale of planned removals would raise logistical, financial and diplomatic challenges and would be vigorously challenged in court. But there is no mistaking the breadth and ambition of the shift Mr. Trump is eyeing.

In a second Trump presidency, the visas of foreign students who participated in anti-Israel or pro-Palestinian protests would be canceled. U.S. consular officials abroad will be directed to expand ideological screening of visa applicants to block people the Trump administration considers to have undesirable attitudes. People who were granted temporary protected status because they are from certain countries deemed unsafe, allowing them to lawfully live and work in the United States, would have that status revoked.

Similarly, numerous people who have been allowed to live in the country temporarily for humanitarian reasons would also lose that status and be kicked out, including tens of thousands of the Afghans who were evacuated amid the 2021 Taliban takeover and allowed to enter the United States. Afghans holding special visas granted to people who helped U.S. forces would be revetted to see if they really did.

And Mr. Trump would try to end birthright citizenship for babies born in the United States to undocumented parents — by proclaiming that policy to be the new position of the government and by ordering agencies to cease issuing citizenship-affirming documents like Social Security cards and passports to them. That policy’s legal legitimacy, like nearly all of Mr. Trump’s plans, would be virtually certain to end up before the Supreme Court.

In interviews with The New York Times, several Trump advisers gave the most expansive and detailed description yet of Mr. Trump’s immigration agenda in a potential second term. In particular, Mr. Trump’s campaign referred questions for this article to Stephen Miller, an architect of Mr. Trump’s first-term immigration policies who remains close to him and is expected to serve in a senior role in a second administration.

All of the steps Trump advisers are preparing, Mr. Miller contended in a wide-ranging interview, rely on existing statutes; while the Trump team would likely seek a revamp of immigration laws, the plan was crafted to need no new substantive legislation. And while acknowledging that lawsuits would arise to challenge nearly every one of them, he portrayed the Trump team’s daunting array of tactics as a “blitz” designed to overwhelm immigrant-rights lawyers.

“Any activists who doubt President Trump’s resolve in the slightest are making a drastic error: Trump will unleash the vast arsenal of federal powers to implement the most spectacular migration crackdown,” Mr. Miller said, adding, “The immigration legal activists won’t know what’s happening.”

Todd Schulte, the president of FWD.us, an immigration and criminal justice advocacy group that repeatedly fought the Trump administration, said the Trump team’s plans relied on “xenophobic demagoguery” that appeals to his hardest-core political base.

“Americans should understand these policy proposals are an authoritarian, often illegal, agenda that would rip apart nearly every aspect of American life — tanking the economy, violating the basic civil rights of millions of immigrants and native-born Americans alike,” Mr. Schulte said.

‘Poisoning the Blood’

Since Mr. Trump left office, the political environment on immigration has moved in his direction. He is also more capable now of exploiting that environment if he is re-elected than he was when he first won election as an outsider.

The ebbing of the Covid-19 pandemic and resumption of travel flows have helped stir a global migrant crisis, with millions of Venezuelans and Central Americans fleeing turmoil and Africans arriving in Latin American countries before continuing their journey north. Amid the record numbers of migrants at the southern border and beyond it in cities like New York and Chicago, voters are frustrated and even some Democrats are calling for tougher action against immigrants and pressuring the White House to better manage the crisis.

Mr. Trump and his advisers see the opening, and now know better how to seize it. The aides Mr. Trump relied upon in the chaotic early days of his first term were sometimes at odds and lacked experience in how to manipulate the levers of federal power. By the end of his first term, cabinet officials and lawyers who sought to restrain some of his actions — like his Homeland Security secretary and chief of staff, John F. Kelly — had been fired, and those who stuck with him had learned much.

In a second term, Mr. Trump plans to install a team that will not restrain him.

Since much of Mr. Trump’s first-term immigration crackdown was tied up in the courts, the legal environment has tilted in his favor: His four years of judicial appointments left behind federal appellate courts and a Supreme Court that are far more conservative than the courts that heard challenges to his first-term policies.

The fight over Deferred Action for Childhood Arrivals provides an illustration.

DACA is an Obama-era program that shields from deportation and grants work permits to people who were brought unlawfully to the United States as children. Mr. Trump tried to end it, but the Supreme Court blocked him on procedural grounds in June 2020.

Mr. Miller said Mr. Trump would try again to end DACA. And the 5-4 majority of the Supreme Court that blocked the last attempt no longer exists: A few months after the DACA ruling, Justice Ruth Bader Ginsburg died and Mr. Trump replaced her with a sixth conservative, Justice Amy Coney Barrett.

Mr. Trump’s rhetoric has more than kept up with his increasingly extreme agenda on immigration.

His stoking of fear and anger toward immigrants — pushing for a border wall and calling Mexicans rapists — fueled his 2016 takeover of the Republican Party. As president, he privately mused about developing a militarized border like Israel’s, asked whether migrants crossing the border could be shot in the legs and wanted a proposed border wall topped with flesh-piercing spikes and painted black to burn migrants’ skin.

As he has campaigned for the party’s third straight presidential nomination, his anti-immigrant tone has only grown harsher. In a recent interview with a right-wing website, Mr. Trump claimed without evidence that foreign leaders were deliberately emptying their “insane asylums” to send the patients across America’s southern border as migrants. He said migrants were “poisoning the blood of our country.” And at a rally on Wednesday in Florida, he compared them to the fictional serial killer and cannibal Hannibal Lecter, saying, “That’s what’s coming into our country right now.”

Mr. Trump had similarly vowed to carry out mass deportations when running for office in 2016, but the government only managed several hundred thousand removals per year under his presidency, on par with other recent administrations. If they get another opportunity, Mr. Trump and his team are determined to achieve annual numbers in the millions.

Keeping People Out

Mr. Trump’s immigration plan is to pick up where he left off and then go much farther. He would not only revive some of the policies that were criticized as draconian during his presidency, many of which the Biden White House ended, but also expand and toughen them.

One example centers on expanding first-term policies aimed at keeping people out of the country. Mr. Trump plans to suspend the nation’s refugee program and once again categorically bar visitors from troubled countries, reinstating a version of his ban on travel from several mostly Muslim-majority countries, which President Biden called discriminatory and ended on his first day in office.

Mr. Trump would also use coercive diplomacy to induce other nations to help, including by making cooperation a condition of any other bilateral engagement, Mr. Miller said. For example, a second Trump administration would seek to re-establish an agreement with Mexico that asylum seekers remain there while their claims are processed. (It is not clear that Mexico would agree; a Mexican court has said that deal violated human rights.)

Mr. Trump would also push to revive “safe third country” agreements with several nations in Central America, and try to expand them to Africa, Asia and South America. Under such deals, countries agree to take would-be asylum seekers from specific other nations and let them apply for asylum there instead.

While such arrangements have traditionally only covered migrants who had previously passed through a third country, federal law does not require that limit and a second Trump administration would seek to make those deals without it, in part as a deterrent to migrants making what the Trump team views as illegitimate asylum claims.

At the same time, Mr. Miller said, the Centers for Disease Control and Prevention would invoke the public health emergency powers law known as Title 42 to again refuse to hear any asylum claims by people arriving at the southern border. The Trump administration had internally discussed that idea early in Mr. Trump’s term, but some cabinet secretaries pushed back, arguing that there was no public health emergency that would legally justify it. The administration ultimately implemented it during the coronavirus pandemic.

Saying the idea has since gained acceptance in practice — Mr. Biden initially kept the policy — Mr. Miller said Mr. Trump would invoke Title 42, citing “severe strains of the flu, tuberculosis, scabies, other respiratory illnesses like R.S.V. and so on, or just a general issue of mass migration being a public health threat and conveying a variety of communicable diseases.”

Mr. Trump and his aides have not yet said whether they would re-enact one of the most contentious deterrents to unauthorized immigration that he pursued as president: separating children from their parents, which led to trauma among migrants and difficulties in reuniting families. When pressed, Mr. Trump has repeatedly declined to rule out reviving the policy. After an outcry over the practice, Mr. Trump ended it in 2018 and a judge later blocked the government from putting it back into effect.

Mass Deportations

Soon after Mr. Trump announced his 2024 campaign for president last November, he met with Tom Homan, who ran ICE for the first year and a half of the Trump administration and was an early proponent of separating families to deter migrants.

In an interview, Mr. Homan recalled that in that meeting, he “agreed to come back” in a second term and would “help to organize and run the largest deportation operation this country’s ever seen.”

Trump advisers’ vision of abrupt mass deportations would be a recipe for social and economic turmoil, disrupting the housing market and major industries including agriculture and the service sector.

Mr. Miller cast such disruption in a favorable light.

“Mass deportation will be a labor-market disruption celebrated by American workers, who will now be offered higher wages with better benefits to fill these jobs,” he said. “Americans will also celebrate the fact that our nation’s laws are now being applied equally, and that one select group is no longer magically exempt.”

One planned step to overcome the legal and logistical hurdles would be to significantly expand a form of fast-track deportations known as “expedited removal.” It denies undocumented immigrants the usual hearings and opportunity to file appeals, which can take months or years — especially when people are not in custody — and has led to a large backlog. A 1996 law says people can be subject to expedited removal for up to two years after arriving, but to date the executive branch has used it more cautiously, swiftly expelling people picked up near the border soon after crossing.

The Trump administration tried to expand the use of expedited removal, but a court blocked it and then the Biden team canceled the expansion. It remains unclear whether the Supreme Court will rule that it is constitutional to use the law against people who have been living for a significant period in the United States and express fear of persecution if sent home.

Mr. Trump has also said he would invoke an archaic law, the Alien Enemies Act of 1798, to expel suspected members of drug cartels and criminal gangs without due process. That law allows for summary deportation of people from countries with which the United States is at war, that have invaded the United States or that have engaged in “predatory incursions.”

The Supreme Court has upheld past uses of that law in wartime. But its text seems to require a link to the actions of a foreign government, so it is not clear whether the justices will allow a president to stretch it to encompass drug cartel activity.

More broadly, Mr. Miller said a new Trump administration would shift from the ICE practice of arresting specific people to carrying out workplace raids and other sweeps in public places aimed at arresting scores of unauthorized immigrants at once.

To make the process of finding and deporting undocumented immigrants already living inside the country “radically more quick and efficient,” he said, the Trump team would bring in “the right kinds of attorneys and the right kinds of policy thinkers” willing to carry out such ideas.

And because of the magnitude of arrests and deportations being contemplated, they plan to build “vast holding facilities that would function as staging centers” for immigrants as their cases progress and they wait to be flown to other countries.

Mr. Miller said the new camps would likely be built “on open land in Texas near the border.”

He said the military would construct them under the authority and control of the Department of Homeland Security. While he cautioned that there were no specific blueprints yet, he said the camps would look professional and similar to other facilities for migrants that have been built near the border.

Such camps could also enable the government to speed up the pace and volume of deportations of undocumented people who have lived in the United States for years and so are not subject to fast-track removal. If pursuing a long-shot effort to win permission to remain in the country would mean staying locked up in the interim, some may give up and voluntarily accept removal without going through the full process.

The use of these camps, Mr. Miller said, would likely be focused more on single adults because the government cannot indefinitely hold children under a longstanding court order known as the Flores settlement. So any families brought to the facilities would have to be moved in and out more quickly, he said.

The Trump administration tried to overturn the Flores settlement, but the Supreme Court did not resolve the matter before Mr. Trump’s term ended. Mr. Miller said the Trump team would try again.

To increase the number of agents available for ICE sweeps, Mr. Miller said, officials from other federal law enforcement agencies would be temporarily reassigned, and state National Guard troops and local police officers, at least from willing Republican-led states, would be deputized for immigration control efforts.

While a law known as the Posse Comitatus Act generally forbids the use of the armed forces for law enforcement purposes, another law called the Insurrection Act creates an exception. Mr. Trump would invoke the Insurrection Act at the border, enabling the use of federal troops to apprehend migrants, Mr. Miller said.

“Bottom line,” he said, “President Trump will do whatever it takes.”