President Donald Trump on Tuesday suggested he will order military forces to the U.S.-Mexico border to secure it and appeared to shrink his border wall requirement to 800 miles.

“We are going to be guarding our border with our military,” he told reporters alongside leaders of Baltic countries at the White House. “That’s a big step.”

At a joint press conference afterward with the Baltic leaders, Trump said he would be meeting with Defense Secretary James Mattis later Tuesday about the idea.

“We have to have strong borders,” he said.

A section of the United States code prohibits a sitting president from using the military as a police force, and border security is a law enforcement function. The president could have been referring to National Guard troops.

Watch: Trump’s Tweets Won’t Help Score a Border Security Deal with Congress

The part of the U.S. code that prohibits military forces doing police tasks can be waived — by an act of Congress. But with Democrats able to hold up legislation in the Senate, that appears unlikely.

A 2012 Congressional Research Service report noted that the Posse Comitatus Act “outlaws the willful use of any part of the Army or Air Force to execute the law unless expressly authorized by the Constitution or an act of Congress” — but also that “express statutory exceptions include the legislation that allows the President to use military force to suppress insurrection or to enforce federal authority … and laws that permit the Department of Defense to provide federal, state and local police with information, equipment, and personnel.”

During the 1993 siege of the Branch Davidian compound near Waco, Texas, the military provided federal agents with equipment that included several Bradley armored personnel carriers and two M1 Abrams tanks. National Guard units also deployed helicopters and surveillance aircraft. But active-duty troops and National Guardsmen reportedly did not participate directly in the assault. Four agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives and more than 80 people in the compound were killed before the standoff ended. 

And in 1997, 18-year-old Esequiel Hernandez Jr., who was herding goats in Texas near the Rio Grande, was killed in an encounter with four U.S. Marines on a a drug-surveillance mission.

Blaming Obama

Trump on Tuesday also blamed his predecessor for his perceived immigration woes: “President [Barack] Obama made changes that basically created no border.” 

“We cannot have people flowing into our country illegally, disappearing, and by the way never showing up for court,” he said, referring to so-called catch-and-release policies. The remarks came after he fired off a string of tweets over the last 48 hours about immigration — many of which a Roll Call analysis found to be factually incorrect.

Watch: Ryan Defends Lack of Border Wall Funding in Omnibus Spending Plan

The president also appeared to give a vote of confidence to embattled EPA Administrator Scott Pruitt, saying: “I hope he’s going to be great.”

Other Cabinet officials and senior aides, however, have received similar positive comments while under fire, only to be dismissed later.

Megan Scully contributed to this report.