A war of words erupted Monday between Gov. Gavin Newsom and the White House, punctuated by President Trump saying that the governor should be arrested because “he’s done such a bad job” leading California.

The latest feud came after a weekend of clashes in Los Angeles as residents protested federal immigration raids and President Trump’s decision to deploy National Guard troops without support from Mr. Newsom.

Mr. Trump has criticized Mr. Newsom on various issues for months, including his handling of the Los Angeles fires and California’s transgender athlete policy. Mr. Newsom had, for the most part, sparingly struck back while still trying to show deference to the president.

But that ended this weekend. And by Monday, the governor was firing back with a barrage of social media posts, emails and news interviews, in a tone that ranged from snarky to serious.

All of it was suited for an era of politics that rewards jousting by online gladiators.

The latest skirmish began when Mr. Trump’s border czar, Tom Homan, told NBC News on Saturday that he would arrest anybody, including Mr. Newsom, who interfered with immigration enforcement.

The governor responded with a dare for Mr. Homan.

“Come after me,” Mr. Newsom said in an interview with MSNBC on Sunday. “Arrest me, tough guy. Let’s just get it over with.”

Reporters then asked Mr. Trump on Monday if he thought Mr. Homan should arrest Mr. Newsom.

“I would do it if I were Tom,” Mr. Trump said. “Look, I like Gavin Newsom, he’s a nice guy. But he’s grossly incompetent.”

Mr. Newsom responded by sharing on X a video of the president’s comments— and pinned it to the top of his feed to give it extra prominence.

“The President of the United States just called for the arrest of a sitting Governor. This is a day I hoped I would never see in America,” he wrote, calling it an “unmistakable step toward authoritarianism.”

Later Monday, a reporter asked Mr. Trump what crime Mr. Newsom should be charged with if he were to be arrested.

“His primary crime is running for governor, because he’s done such a bad job,” Mr. Trump said. “What he’s done to that state is like what Biden did to this country.”

Mr. Newsom posted that video, too. He added social media posts that needled Mr. Trump’s Republican supporters, including Vice President JD Vance, Senator Tommy Tuberville of Alabama and Representative Jim Jordan of Ohio.

Mr. Jordan posted a comment on X saying, “We fly the American flag in America” — an apparent reference to the many Latin American flags that demonstrators carried at the protests in Los Angeles. Mr. Newsom shot back with a photo of Jan. 6 protesters on the steps of the U.S. Capitol, one of them attacking police officers with an American flag.

“Like this?” Mr. Newsom wrote.