What will be the US military's role in Trump's mass deportation plan?

The Trump administration's plan to use active-duty U.S. military personnel to help with the mass deportation of undocumented migrants appears to be similar to the support role that troops provided along the U.S-Mexico border in 2018 and 2019, during the first Trump administration.

During his 2024 campaign, President-elect Donald Trump often referenced military personnel forming a part of his plans to assist the deportation, but how they would do that under existing legal authorities was left vague. On Monday, however, Trump confirmed that he planned to declare a national emergency to carry out that campaign promise.

Additionally, Thomas Homan, Trump's choice to serve as the Border Czar, fleshed out his view of how U.S. military assets would be a "force multiplier" in the deportations but stressed that they would be carrying out "non-enforcement duties." In other words, military personnel will not be participating in arrests.

"They'll be used to do non-enforcement duties such as transportation, whether it's on ground or air, infrastructure, building, intelligence," Homan said in an interview on Fox Business Network.

U.S. Immigration and Customs Enforcement (ICE) officers doing those duties could be replaced by military personnel "because it doesn't require immigration authority," Homan explained.

He also described the military's role as a "force multiplier to take more agents, put them on streets where we need them" and he envisioned the U.S. military possibly assisting in flights taking detainees back to their home countries.

"We're hoping DOD will help us with air flights, because there's a limited number of planes ICE has contracts with; so DOD can certainly help with air flights all across the globe," he said.

Homan's description was very similar to the previous active-duty deployment in 2018 and 2019 ,during Trump's first term that supported U.S. Customs and Border Protection (CBP) as migrant caravans from Central America made their way to the U.S. border.

The mission was ordered in October 2018 and eventually saw the deployment of 6,100 active duty forces to the border, which was soon followed by Trump's declaration of a national emergency that enabled the U.S. military to help build portions of the border wall.

Pentagon officials stressed that the thousands of active-duty troops deployed to the border would only be serving in a support role to federal law enforcement and that they would not carry out law enforcement duties. That role was in line with the Posse Comitatus Act that forbids the U.S. military from carrying out law enforcement duties domestically.

The active-duty troops joined 2,350 National Guardsmen who were already helping CBP in their home states of California, Texas, and Arizona.

Initially, the mission of the active-duty troops was to build housing for additional CBP personnel headed to the region, provide medical support, fly CBP personnel around the border region and construct 70 miles of additional obstacles and security barriers for the 22 ports of entry. Military police units were deployed to provide security for military construction crews working along the border and were the only forces that were allowed to be armed during the deployment.

What was supposed to be a 45-day mission kept being extended and continues to this day in a modified way and in much smaller numbers than 2019.

After the initial mission goals were quickly completed, the Pentagon approved a new Department of Homeland Security request to set up an unarmed quick reaction force to help CPB with riot control in case there was a migrant rush at a port of entry.

In April 2019, the role of active-duty troops was expanded so they could be allowed to assist in driving high-capacity CBP vehicles to transport migrants; provide administrative support, including providing heating, meal distribution and monitoring the welfare of individuals in CBP custody; and attorney support to ICE.

A month later, the Pentagon approved a DHS request to provide tent housing for up to 7,500 single adult migrants at six locations along the border. The tents were to come from U.S. military supplies and were to be erected by U.S. military personnel. . Eventually, DHS requested that active duty personnel set up an additional 150 miles of concertina wire along the border area beyond the 70 miles of obstacles that were laid out in the first six weeks of the border support mission.

Trump's conformation that he plans to declare a national emergency to enable the mass deportation is a different rationale than the national emergency that he declared in 2019.

The 6,100 active-duty troops were deployed to the border under existing authorities. Instead, the national emergency that Trump declared in early 2019 was to make it possible for the U.S military to help construct portions of the border wall that had been one of his major campaign promises.

The National Emergencies Act allows the military to undertake new military construction projects not specified by Congress, but only if previously appropriated funds for such projects are used.

In the end, the Pentagon was able to use $6.1 billion in funding for the wall including $3.6 billion in funds reallocated from other projects and an additional $2.5 billion in funding from counter narcotics efforts.

Declaring a national emergency is not a rare occurrence and the National Emergencies Act has been invoked multiple times. At the time of the border declaration, there were about 30 emergencies already in effect by previous administrations.