The Pentagon will begin deploying as many as 1,500 active-duty troops to help secure the southern border in the coming days, the White House confirmed Wednesday, putting in motion plans President Donald Trump laid out in executive orders shortly after he took office to crack down on immigration.

Acting Defense Secretary Robert Salesses was expected to sign the deployment orders Wednesday, but it wasn't yet clear which troops would go, and the total could fluctuate. It remains to be seen if they will end up doing law enforcement, which would put American troops in a dramatically different role for the first time in decades.

"This is something President Trump campaigned on," said Karoline Leavitt, White House press secretary. "The American people have been waiting for such a time as this — for our Department of Defense to actually implement homeland security seriously. This is a No. 1 priority for the American people."

The active-duty forces will join the roughly 2,500 U.S. National Guard and Reserve forces already there. There are currently no active-duty troops working along the roughly 2,000-mile border.

The troops are expected to be used to support Border Patrol agents, with logistics, transportation and construction of barriers, according to U.S. officials, who spoke on condition of anonymity because details have not yet been released. Troops have done similar duties in the past, when both Trump and former President Joe Biden sent active-duty troops to the border.

Troops are prohibited by law from doing law enforcement duties under the Posse Comitatus Act, but that may change. Trump has directed through executive order that the incoming secretary of defense and incoming homeland security chief report back within 90 days if they think an 1807 law called the Insurrection Act should be invoked. That would allow those troops to be used in civilian law enforcement on U.S. soil.

The last time the act was invoked was in 1992 during rioting in Los Angeles in protest of the acquittal of four police officers charged with beating Rodney King.

The widely expected deployment, coming in Trump's first week in office, was an early step in his long-touted plan to expand the use of the military along the border. In one of his first orders on Monday, Trump directed the defense secretary to come up with a plan to "seal the borders" and repel "unlawful mass migration."

On Tuesday, just as Trump fired the Coast Guard commandant, Admiral Linda Fagan, the service announced it was surging more cutter ships, aircraft and personnel to the "Gulf of America" — a nod to the president's directive to rename the Gulf of Mexico.

Military personnel have been sent to the border almost continuously since the 1990s to help address migration, drug trafficking and transnational crime.

In executive orders signed Monday, Trump suggested the military would help the Department of Homeland Security with "detention space, transportation (including aircraft), and other logistics services."

There are about 20,000 Border Patrol agents, and while the southern border is where most are located, they're also responsible for protecting the northern border with Canada. Usually, agents are tasked with looking for drug smugglers or people trying to enter the country undetected.

More recently, however, they have had to deal with migrants actively seeking out Border Patrol in order to get refuge in America — taxing the agency's staff.

In his first term, Trump ordered active-duty troops to the border in response to a caravan of migrants slowly making its way through Mexico toward the United States in 2018. More than 7,000 active-duty troops were sent to Texas, Arizona and California, including military police, an assault helicopter battalion, various communications, medical and headquarters units, combat engineers, planners and public affairs units.

At the time, the Pentagon was adamant that active-duty troops would not do law enforcement. So they spent much of their time transporting Border Patrol agents to and along the border, helping them erect additional vehicle barriers and fencing along the border, assisting them with communications and providing some security for border agent camps.

The military also provided Border Patrol agents with medical care, pre-packaged meals and temporary housing.