President Trump said on Monday that he would invoke the Insurrection Act in Portland if necessary.

“Portland is on fire. Portland’s been on fire for years, and that’s not so much saving it. We have to save something else, because I think that’s all insurrection,” Mr. Trump told reporters at the White House. “I really think that’s criminal insurrection.”

Mr. Trump said he would do what “was necessary” if it came down to invoking the Insurrection Act in Portland.

“So far it hasn’t been necessary. But we have an Insurrection Act for a reason. If I had to enact it, I’d do that if people were being killed, and courts were holding us up, or governors or mayors were holding us up,” he said. “Sure. I would do that. I want to make sure that people aren’t killed. We have to make sure that our cities are safe.”

The Insurrection Act of 1807 is a federal law that allows for the president to deploy the U.S. military or federalize state National Guard troops to quash what the president sees as an insurrection against the U.S.

This law is an exception to the Posse Comitatus Act, which, by and large, prohibits the use of the military for civilian law enforcement.

The last president to invoke the Insurrection Act was George H.W. Bush during the 1992 Los Angeles riots. 

The other instance was in 1989, in response to looting and unrest in the U.S. Virgin Islands following Hurricane Hugo.

Earlier Monday, White House deputy chief of staff Stephen Miller said the administration had been facing a “legal insurrection” and that rulings stifling the White House’s agenda are “an insurrection against the laws and Constitution of the United States.”

Although Mr. Trump has deployed the National Guard to Washington D.C., Memphis and has attempted to send Guardsmen to other cities, including Portland and Chicago, his administration is facing legal obstacles as Democratic governors are legally challenging federal authority to keep the National Guard out of their states.

White House Press Secretary Karoline Leavitt on Monday called the opinion of the judge who blocked President Trump from deploying National Guard troops to Portland “untethered in reality.”

Ms. Leavitt also said the decision of Judge Karin Immergut, a Trump appointee, risked spiraling the country into an unconstitutional form of “martial law.”

“With all due respect to that judge, I think her opinion is untethered in reality and in the law. The president is using his authority as commander in chief,” Ms. Leavitt said at a White House press briefing.

She cited U.S. Code 12-406, which allows the president to call National Guard units into federal service to repel invasions, suppress rebellions, or execute the laws of the U.S., when regular forces are insufficient to do so.