Donald Trump recaptured the White House after promising policies that included a militarized, mass deportation of undocumented immigrants — a costly undertaking that would probably face immediate legal and logistic challenges.

His election victory sets the stage for a sharp turn in immigration and border policy that could upend millions of lives and recast the U.S. economy and labour force.

The record numbers of illegal border crossings during President Joe Biden’s term appeared to be a drag on Vice President Kamala Harris, whose abbreviated presidential campaign was unable to overcome years of Republican criticism about the scale of migrant arrivals at the U.S.-Mexico border.

Trump said in his victory speech early Wednesday that voters had given him a “powerful mandate” for his agenda, including a border crackdown, with his party potentially in control of both houses of Congress. The dark, violent imagery he wielded on the campaign trail was largely absent from his remarks, and he appeared to appeal to business owners anxious about the labour implications of his deportation plans.

“We’re going to have to seal up those borders,” Trump said. “We want people to come back in … but they have to come in legally.”

Trump started his first presidency in 2017 pledging to deport millions of immigrants, but he fell far short of that goal as his administration faced resource constraints, legal challenges and a public outcry over more-extreme tactics, including the separation of migrant children from their parents.

Trump is expected to bring back many of the same officials who attempted to carry out those harsh policies during his first term.

Chad Wolf, who was acting homeland security secretary at the end of Trump’s first term and who has been mentioned as a possible return candidate, said Trump will have more latitude to make sweeping changes to immigration policy because voters have repudiated the “chaos” at the border under Biden.

“The environment we’re operating in is very different than it was in 2017 and 2018,” Wolf said in an interview. “I think the American people as a whole are much more open to his policies because they’ve seen what’s happened over last four years. The president has a mandate for border security.”

Wolf said he expects Trump to streamline deportations from the interior of the United States, where about 11 million undocumented immigrants reside. He said the Trump administration could curb appeals and quickly rescind Biden policies that limit deportations mostly to serious criminals and recent border-crossers.

“You’ll see a different mindset, and over time it’ll be possible to remove large numbers of people,” he said.

Longtime Trump adviser and speechwriter Stephen Miller is expected to drive immigration policy in the White House, as he did during Trump’s first term. Miller did not respond Wednesday to a request for comment.

Tom Homan, who was acting director of U.S. Immigration and Customs Enforcement from January 2017 to June 2018, is also a leading candidate for a high-level position. He told CBS News’s “60 Minutes” last month that a mass deportation plan would prioritize the arrest of criminals and national security threats, as it has for decades.

Homan also said anyone in the United States illegally could be kicked out. He said he would restart workplace enforcement to find people working illegally in the United States and deport them. The Biden administration ended the raids, which Homan said made it easier for employers to hire unauthorized workers, including children.

Homan and Miller were key architects of the “zero tolerance” policy that separated thousands of children from their parents in the first Trump administration, galvanizing advocacy groups, which helped elect Biden and shaped his immigration agenda. Democratic-leaning jurisdictions embraced “sanctuary” policies limiting police cooperation with ICE. Their opposition could once more hamper the government’s ability to sweep up potential deportees.

Trump has pledged to quickly recommence construction of the border wall. The Department of Homeland Security has about $1 billion in construction funds left from Trump’s first term, and some supplies remain stockpiled along the border where they were left when Biden froze the project in January 2021.

Trump is expected to move quickly to rescind Biden administration programs that have relied on executive authority to dramatically expand opportunities for migrants to live and work temporarily in the United States. More than 500,000 migrants from Cuba, Haiti, Nicaragua and Venezuela have been allowed to enter the country lawfully under Biden, and many will be at risk of losing their legal status if Trump revokes their protections.

Lawyers and organizers said they have been preparing for months to restart the resistance that foiled Trump’s first-term efforts to deport millions.

These advocates are drafting lawsuits to block his policies, preparing to defend immigrants against deportation proceedings, and scheduling mass education campaigns to inform people about their rights if they are detained.

After the election results rolled in, some groups urged Biden to capitalize on his final months in office to extend work permits and temporary protections to the millions of undocumented immigrants in the country, to give them some support during Trump’s first months in office.

Advocates acknowledged that Republican opposition to the border surge and the Texas governor’s busing of thousands of immigrants to Democrat-led cities have eroded support for immigrant protections. Unlike past migrant influxes, the arrivals under Biden often lacked relatives in the United States and at first relied on cities and towns to provide shelter and food at a cost of billions of dollars.

Gustavo Torres, president of Casa in Action, an immigrant rights group, said the economy was a “clear factor” in Trump’s victory. But Torres said that immigrants remain a vital part of the economy and that cities and towns would continue to protect them.

“We’re going to keep organizing,” he said as he rushed to an emergency meeting Wednesday in Maryland with immigrants from Latin America and Africa, who are fearful of being deported.

“People are very frightened,” he said. “They don’t know what is going to happen. … We have to prepare for the worst.”

Tom Warrick, a former Department of Homeland Security official who has served under Republican and Democratic administrations, said Homan, Miller and others in Trump’s orbit are intimately familiar with the limitations of U.S. deportation capacity — including detention space, aircraft and diplomatic strains with countries such as Venezuela and Nicaragua that limit or refuse to accept removal flights.

“The sheer size of what they’re planning will be limited by resources,” Warrick said. “The question is what is Trump pushing for, and how fast is he pushing the system, and what is he going to do about people with judicial orders that say their asylum claims must be heard.”

“If they plan on limiting the number of arrests to keep the system at capacity — but not over capacity — they will be able to keep popular support a lot longer than if people see pictures that look like Japanese internment camps from the 1940s,” Warrick said.

Illegal crossings along the southern border averaged 2 million during Biden’s first three years in office, peaking in December 2023 with nearly 250,000 arrests, the highest one-month total on record. Crossings are down 78% since then, the result of tougher enforcement targeting migrants travelling through Mexico and emergency measures imposed this year that deny migrants access to the U.S. asylum system.

Critics say Biden’s border policy pivot came too late to help Harris.

Trump demonized immigrants on the campaign trail, spreading false claims that nations were emptying their prisons and mental hospitals into the United States. These migrants, he said, were “poisoning the blood” of the United States, statements echoing Nazi rhetoric.

Trump’s victory speech was less dour, leaving open a door for immigrants seeking to come legally. He has backed a plan that would create a Canada-style merit-based system for high-skilled immigrants. He said he would “end chain migration,” a derisive term for the system that for decades has made it a priority to bring in the immediate relatives of U.S. citizens, including his in-laws from Slovenia.

Trump campaigned on the idea that the mass deportation of undocumented immigrants would lead to more jobs and higher wages for American workers. But studies of large-scale deportations have found that these expulsions serve only to lower employment levels and wages for U.S.-born workers.

“Eight million undocumented people are currently earning hundreds of billions and spending hundreds of billions on food, clothing, shelter,” said Robert Lynch, a professor emeritus of Economics at Washington College.

“If you remove those people from the economy, American businesses will sell less,” Lynch said. “When they sell less, they going to produce less and will need fewer workers and lay off workers. Incomes will fall.”

Many economists also say that mass deportations on the scale proposed by Trump would trigger inflation in the short term — by forcing employers dealing with labour shortfalls to raise prices. A major deportation program would also shrink the economy by 2.6% to 6.2% a year, according to a recent review of projections published by the University of New Hampshire.

Trump has repeatedly pledged to invoke the Alien Enemies Act of 1798, a wartime authority that allows the president to quickly deport foreign nationals without a hearing, according to an analysis by the Brennan Center for Justice, a think tank.

He has said he would prioritize the arrests of criminals such as members of the Venezuelan street gang Tren de Aragua and the U.S.-Salvadoran MS-13 gang.

Trump, speaking at a rally Monday, also promised to ban sanctuary cities in the United States, an effort that failed during his first term, and he called for the death penalty for any migrant who kills an American citizen or law enforcement officer.

Trump has not ruled out restoring detention for migrant families, which Biden ended, and he has not given a clear answer on whether he would again try to separate migrant parents and children.

“As bad as the first Trump administration was for immigrants, we anticipate it will be much worse this time and are particularly concerned about the use of the military to round up immigrants,” said Lee Gelernt, a lawyer with the American Civil Liberties Union who challenged family-separation and other Trump policies in court. “As always, we will go to court to challenge illegal policies, but it is equally essential that the public push back, as it did with family separation.”

“We have no choice other than to fight,” Gelernt said.

— Lauren Kaori Gurley contributed to this report.