Days of sometimes violent unrest in Downtown Los Angeles — prompted by widespread federal immigration raids that began late last week — has sparked a confrontation between the Republican commander in chief and the Democratic governor of the nation’s largest state over presidential authority to call up National Guard forces.

President Trump decided to call in federal forces on Sunday after several blocks of the downtown area erupted in violence resulting in vandalism, burning cars, and skirmishes with law enforcement. Los Angeles’ mayor, Karen Bass, and Governor Newsom described the events as mostly peaceful and declined to request federal support, leading to a clash over the president’s authority. 

“It’s lucky for the people in Los Angeles and in California that we did what we did, we got it just in time. It’s still simmering a little bit. But not very much,” Mr. Trump said late Monday during a press briefing at the White House. “I’m very happy I got involved and I think Gavin in his own way is probably happy I got involved. “

Mr. Newsom, however, did not appear happy on Monday morning, announcing along with California Attorney General Rob Bonta, that the state would file a lawsuit against Mr. Trump, accusing him and Defense Secretary Pete Hegseth of violating the 10th Amendment and that they would ask a federal judge to put a stop to the “unlawful, unprecedented”deployment of the National Guard.

“Federalizing the California National Guard is an abuse of the president’s authority under the law, and not one we take lightly,” Mr. Bonta said in the statement.

The president has limited authority to call up troops on domestic territory unless a governor requests the assistance or he invokes the Insurrection Act, an 1807 law that allows him to tamp down civil unrest. The president referred to rioters as insurrectionists, though stepped shy of invoking the law. 

He also suggested that the California governor should be arrested for obstructing Immigration and Customs enforcement chief Tom Homan.

“I would do it if I were Tom,” Mr. Trump said, responding to a reporter’s question about arresting the governor. “I think it’s great. Gavin likes the publicity. But I do think it would be a great thing.”

Mr. Newsom quickly responded to the comments in a post on X.

“The President of the United States just called for the arrest of a sitting Governor,” he said. “This is a day I hoped I would never see in America. I don’t care if you’re a Democrat or a Republican, this is a line we cannot cross as a nation — this is an unmistakable step toward authoritarianism.”

Mr. Trump later walked back the idea of taking Mr. Newsom into custody.

“What crime has he committed? I think he’s primarily, his primary crime is running for governor because he’s done such a bad job,” Mr, Trump said referring to Mr. Newsom. “What he’s done to that state is like what Biden did to this country and that’s pretty bad.”

Hundreds of active-duty Marines from Camp Pendleton remained on standby late Monday after the Defense Department said it will act solely in a support capacity if rioting continues.