Amid a mounting legal clash between the federal government and the state of California, President Donald Trump suggested his border czar Tom Homan should arrest Gov. Gavin Newsom.

“I would do it … I think it would be a great thing,” Trump said June 9 when asked if Homan should arrest the governor, who has challenged the administration’s mobilization of National Guard troops to crack down on violent protests against immigration raids in Los Angeles. The president also attacked Newsom as "grossly incompetent."

Newsom was aghast: "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 said on X.

"I don’t care if you’re a Democrat or a Republican," Newsom wrote. "This is a line we cannot cross as a nation − this is an unmistakable step toward authoritarianism."

Homan previously refused to rule out arresting state and local politicians who impede federal agents.

Arresting Newsom, who responded to Homan’s threat by daring the feds to arrest him in a June 8 social media post, would represent a major escalation of the state’s widening rift with the Trump administration.

Homan, a career law enforcement official and former acting head of ICE, is on the White House payroll and likely does not have direct arrest powers.

Although Trump has legal authority to unilaterally take control of California's Guard troops through a process called "federalization," federalized Guardsmen cannot directly participate in civilian law enforcement unless the president invokes the Insurrection Act. The act allows the president to use military force to suppress rebellion or revolt against the federal government.

Trump hasn't invoked the Insurrection Act amid the Los Angeles unrest. His proclamation federalizing the Guard troops, though, isn't restricted to California and says guardsmen will "protect" ICE and other Department of Homeland Security personnel.

In May, DHS separately requested the activation of 20,000 National Guard members to support immigration enforcement under state-controlled legal authorities that permit direct law enforcement.

This article originally appeared on USA TODAY: 'I would': Trump says he'd arrest California Gov. Gavin Newsom

Reporting by Davis Winkie, USA TODAY / USA TODAY

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