'Acts of a dictator': Newsom lashes out at Trump after arrest threat

President Donald Trump and California's Democratic Gov. Gavin Newsom escalated their confrontation on Monday over the handling of protests in Los Angeles triggered by Trump's immigration crackdown.

After Newsom had objected to Trump sending in the National Guard without his consent, Trump on Monday afternoon ordered hundreds of Marines into the city as well.

Earlier Monday, arriving back at the White House after spending the weekend at Camp David, Trump had told reporters he would arrest Newsom if he were "border czar" Tom Homan -- hours after Homan said there had been "no discussion" about arresting Newsom.

"I would do it if I were Tom. I think it's great," Trump told reporters on the South Lawn.

Newsom quickly fired back.

"The President of the United States just called for the arrest of a sitting Governor," Newsom posted on Instagram along with a video of Trump's comments. "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."

"These are the acts of a dictator, not a President," Newsom posted on X.

At a White House event Monday afternoon, Trump was asked by ABC News White House Correspondent Karen Travers what crime Newsom had committed that would warrant his arrest.

"I think his primary crime is running for governor because he's done such a bad job," Trump responded.

Homan himself earlier Monday pushed back on the idea he was going to arrest Newsom and Los Angeles Mayor Karen Bass, both Democrats.

In an interview with NBC News over the weekend, Homan had not ruled out the possibility -- prompting Newsom to respond: "He knows where to find me."

Homan on Monday morning, during an interview on Fox, commented further on his remarks to NBC.

"The reporter asked about, 'Could Governor, Governor Newsom, or Mayor Bass, be arrested? I said, 'Well, no one's above the law, if they cross the line and commit a crime. Absolutely they can.' So, there was no discussion about arresting Newsom," he said.

"I've said it many times, You can protest, you got your First Amendment rights, but when you cross that line, you put hands on an ICE officer, or you destroy property, or ICE says that you're impeding law enforcement ... That's a crime, and that the Trump administration is not going to tolerate. You cross that line we're gonna see prosecution in the Department of Justice," Homan said.

House Speaker Mike Johnson expressed solidarity with the president after the president suggested Newsom should be arrested.

"I heard that for the first time sitting next to the president when they asked him that question at the White House. I don't know what all that involves, but he gave comment there, and I'll stick by what he said," Johnson said, adding that he also agrees with the Trump's decision to send in the National Guard, predicting it will have a "deterrent effect."

"We have to maintain the rule of law, and if the state and local leaders are unable or unwilling to do so, it is the job of the federal government to step in," Johnson told reporters outside the White House.

Trump on Monday also doubled down on his decision over the weekend to deploy the National Guard to California, over Newsom's objections.

Trump said in 2020 that a request from a governor was needed to send in the National Guard. On Monday, ABC News asked Trump what changed between his statement then and now.

"Well, the biggest change from that statement is we have an incompetent governor," Trump said. Trump contended his administration was "straightening out his problems."

"I mean, I think we have it very well under control. I think it would have been a very bad situation. It was heading in the wrong direction. It's now heading in the right direction," Trump said.

Trump has long expressed a desire to quash protests he considered dangerous by using the military, though the use of federal troops on U.S. soil is mostly prohibited by the 1878 Posse Comitatus Act. Trump deployed the National Guard in this situation under Title 10 of the U.S. Code.

Asked if he would deploy Marines to Los Angeles on Monday, Trump had said "we'll see what happens."

Shortly after the president's comments, a U.S. official confirmed to ABC News 700 Marines from Twentynine Palms, California, had been ordered to assist on the streets of Los Angeles, although it was unclear exactly what role they would play.

Newsom said the state is suing the administration over Trump deploying the National Guard.

"He flamed the fires and illegally acted to federalize the National Guard," Newsom wrote on social media. "The order he signed doesn't just apply to CA. It will allow him to go into ANY STATE and do the same thing. We're suing him."

ABC News' John Parkinson contributed to this report.