How could the U.S. military be used for Trump’s mass deportation plan?

President-elect Donald Trump has vowed to start the largest deportation effort in American history — his signature 2024 campaign promise — as soon as he takes office, signaling this week that he would enlist the help of the U.S. military for the massive operation to deport undocumented immigrants.

Earlier this week, he shared a social media post indicating that he’d declare a national emergency and deploy military assets to carry out deportations. 

Still, how exactly the military would be tapped to carry out this promise of mass deportations is unclear. And there are untested legal questions about involving service members in immigration enforcement operations.

The Department of Defense has provided operational support to immigration and border authorities for decades, under both Republican and Democratic presidents. Roughly 4,000 service members – primarily from the National Guard – are currently authorized to support the U.S. Customs and Border Protection (CBP) security mission along the southwest border, according to the U.S. Northern Command. 

While longstanding federal law generally prohibits the use of the military for domestic law enforcement – which includes immigration arrests and deportations – a few rarely invoked statutory exceptions exist. 

The Department of Defense’s vast funding and resources could be instrumental in helping the incoming administration address the operational and financial challenges of carrying out deportations on a monumental scale. Immigration and Customs Enforcement’s deportation branch has a fraction of the resources that would be necessary, with 6,000 agents and 41,000 detention beds. About 11 million immigrants are estimated to be living in the U.S. illegally.

What have Trump and his allies said about using the military for deportations?

In an interview with CBS’ “60 Minutes” last month, Tom Homan, who Trump has appointed to be his “border czar,” indicated that one way to increase manpower for the mass deportation plan would be to re-hire retired ICE agents. Contractors, he added, could do some of the operational work, including handling transportation and setting up so-called “soft-sided” facilities, or tent detention sites, to hold migrant detainees.

Homan said transportation and supply assets from the Department of Defense would also be helpful, suggesting that military planes could be used for deportation. But Stephen Miller, the incoming White House deputy chief of staff, has gone further than Homan, suggesting the National Guard could be deputized to arrest undocumented immigrants. 

“We will deputize them as immigration enforcement officers,” Miller said during a radio interview last year. “They know their states, they know their communities, they know their cities.”

And while U.S. law generally bans the use of the armed forces for domestic law enforcement, during an interview with the New York Times last year, Miller said a revamped Trump administration would invoke what’s known as the Insurrection Act to create an exception, enabling the use of federal troops to apprehend migrants. 

The military, Miller has also indicated, could be dispatched to the southern border with “an impedance and denial mission.” 

“You reassert the fundamental constitutional principle that you don’t have the right to enter into our sovereign territory, to even request an asylum claim,” Miller said at last year’s CPAC. “The military has the right to establish a fortress position on the border to say no one can cross here at all.” 

Finally, Trump has pledged to use the Alien and Sedition Acts of 1798 — a law invoked during World War II to approve the surveillance and detention of Italian, German, Japanese immigrants — to deport suspected migrant gang members. 

How could the military be deployed to the U.S. border?

The U.S. military’s role at the U.S.-Mexico border dates back to the Mexican American War, with additional buildup of troops at the southern border during the Mexican Revolution and World War I. 

“For basically the past 40 years, the military’s involvement at the border has been steadily growing,” said Joseph Nunn, counsel at the Brennan Center for Justice at New York University’s School of Law, “And it has gone from sort of ad hoc to routine to deeply entrenched into how we approach border security and immigration.” 

Members of the military stationed at the border have historically performed an array of support tasks, experts tell CBS News – from operating surveillance aircrafts and transporting U.S. Border Patrol personnel in helicopters to laying concertina wire and maintaining Customs and Border Protection vehicles. 

Homan’s suggestions of using the military for some of the operational work that doesn’t involve engaging with migrants would fall under this category and would be an expansion of the duties National Guard and a small number of active-duty troops have performed at the southern border under previous administrations. As recently as last year, troops were deployed to the border to help Border Patrol with administrative tasks, like warehouse management and clerical work.

Military involvement now “is just essentially to get access to more bodies and more aircrafts,” Nunn explained, calling military mobilization a force multiplier. “Suppose you want to set up a checkpoint on a highway in Texas or Arizona. Under normal circumstances, you need five CBP agents to run a checkpoint. If you have access to military personnel, you can run a checkpoint with one CBP agent assisted by four soldiers. Then suddenly five CBP agents assisted by soldiers can run five checkpoints instead of one.”

“[The Trump administration] would also use the military to do things like build bases and facilities to hold people,” senior fellow at the Atlantic Council, Thomas Warrick, told CBS News. “He could use the military to fly detainees around the country or indeed to deport them to other countries if they can get landing rights.” 

Can the U.S. military act as domestic law enforcement? 

Using the military in an active law enforcement role, rather than in a support capacity, would be more complex and unusual, but subject to at least one legal loophole. 

The Posse Comitatus Act bars federal armed forces from participating in law enforcement activities unless expressly authorized by Congress. But the 1807 Insurrection Act, which Miller mentioned, allows the president to utilize the military in domestic cases that warrant it. While the National Guard is under state control and not activated for federal service, it is not subject to Posse Comitatus.

Abraham Lincoln used it during the Civil War, and in the 20th century, Dwight D. Eisenhower and John F. Kennedy relied on the law to desegregate schools, deploying troops to the South after the Supreme Court’s landmark decision in Brown v. Board of Education. The most recent time it was used was in 1992 by President George H.W. Bush after both city and state leaders asked for federal help to quell the L.A. riots. 

According to the law, the military may be activated to enforce the laws on U.S. soil or to “suppress rebellion” whenever “unlawful obstructions, combinations, or assemblages, or rebellion” make it “impracticable” to enforce federal law in that state by the “ordinary course of judicial proceedings.”

Can this be challenged in court?

Lee Gelernt, a lawyer at the American Civil Liberties Union, said using the military to carry out deportations under the Alien and Sedition Acts would be “patently unlawful,” because current circumstances don’t allow for it. 

“The law requires an invasion by a foreign government,” said Gelernt, who challenged many of the first Trump administration’s immigration policies. “That’s not what is happening with immigration.”

There already is an agency, ICE, that handles enforcing immigration laws with arrest authority that the U.S. military does not have. 

“It was designed for unexpected emergencies,” Nunn said, but added that, “its text grants vast discretion to the president” with “no meaningful criteria” to justify invoking it.

In 1827, the Supreme Court ruled in Martin v. Mott that the president has the sole authority to decide whether a situation warrants deploying the military. However, “If you can prove that the president has invoked the insurrection act in bad faith, which is going to be a high bar to clear but not impossible, you could potentially challenge the decision to invoke the Insurrection Act,” Nunn explained, adding that the centuries-old law does not permit the military to violate constitutional rights or to violate otherwise applicable federal law.

Peter Feaver, a professor of political science and public policy at Duke University who focuses on civil military relations, said using the military as law enforcement would be controversial and could degrade trust in the military, even if there is a legal case for it. 

“This is not what the military trains for, but on top of all of that, it would be deeply politically polarizing because there’d be many many Americans who would view this as an inappropriate mission, a betrayal of our American values or something,,” said Feaver, who has written a book called “Thanks for Your Service: The Causes and Consequences of Public Confidence in the US Military.” 

Congress has no role in invoking the Insurrection Act. In July, Connecticut Senator Richard Blumenthal, a Democrat, renewed his legislative push to overhaul the law. He first introduced a bill reforming the Insurrection Act in 2020, after Trump’s threats to use troops to respond to civil rights protests across the U.S. following the police killing of George Floyd, but his efforts were stalled by Republican opposition and pushback from the Trump administration. 

What if Trump declared a national emergency at the border?

Trump declared a national emergency at the border during his first administration, after Congress declined to fund border wall construction. He used the declaration to unilaterally divert Pentagon funds to expand the border wall. 

“The Pentagon budget – that’s where the money is,” Warrick said. “It’s where the people are. It’s where the aircrafts are.” 

The long-term cost of deporting 1 million people per year could average $88 billion annually, according to the American Immigration Council, surpassing the Department of Homeland Security’s $62 billion budget in fiscal year 2025 and totalling nearly $968 billion over a decade. The operation would also demand lightning-speed expansion of the immigration court systems and detention facilities. 

“It’s going to be astronomically expensive,” Nunn said. “And not only is it going to be straightforwardly expensive, but it’s also going to come with opportunity costs – every military service member and military asset that is diverted to assist with a mass deportation program or to assist with border security is a service member or asset that is not carrying out their normal duties.”

Caitlin Huey-Burns

contributed to this report.