LOS ANGELES — California officials on Monday said they would file a federal lawsuit over the mobilization of the state’s National Guard during the weekend’s immigration protests in Los Angeles, accusing President Donald Trump of overstepping his federal authority and violating the U.S. Constitution.

As thousands of people gathered in the streets to protest raids and arrests by U.S. Immigration and Customs Enforcement, Trump mobilized nearly 2,000 members of the National Guard over the objections of California Gov. Gavin Newsom, who said state officials could handle the situation and that Trump was sowing chaos in the streets for political purposes.

California Attorney General Rob Bonta said the decision by Trump and U.S. Defense Secretary Pete Hegseth violated the 10th Amendment to the U.S. Constitution, which spells out the limits of federal power. Bonta said the state will seek a restraining order for the “unlawful, unprecedented” deployment.

“Trump and Hegseth ignored law enforcement’s expertise and guidance and trampled over our state’s, California’s, sovereignty,” Bonta said at a Monday press conference.

Experts and state officials say Trump’s actions and the subsequent lawsuit have thrust the U.S. into uncharted legal territory. Bonta said there have not been many court rulings on the questions at play because the statute Trump cited “has been rarely used, for good reason.”

“It is very unusual and unnecessary, and out of keeping with our constitutional tradition, that they are there without the consent of the governor, in a situation where the governor says that state authorities have the situation under control,” said Laura A. Dickinson, a professor at the George Washington University Law School.

Whether Trump’s action was illegal, Dickinson said, “is really untested.”

Trump and the White House say the military mobilization is legal under Section 12406 of Title 10 of the U.S. Code on Armed Services. The statute gives the president the authority to federalize the National Guard if there is “a rebellion or danger of a rebellion against the authority of the government of the United States,” but says the Guard must be called up through an order from the state’s governor.

Trump has said that the mobilization was necessary to “deal with the violent, instigated riots,” and that without the National Guard, “Los Angeles would have been completely obliterated.”

Days of protests after the ICE raids included some violent clashes between protesters, local police and federal officials and some vandalism and burglaries. Local officials have decried those actions but have defended the right of Angelenos to peacefully demonstrate.

“It was heading in the wrong direction,” Trump said Monday at the White House. “It’s now heading in the right direction. And we hope to have the support of Gavin, because Gavin is the big beneficiary as we straighten out his problems. I mean, his state is a mess.”

The part of the law that “the Trump administration is going to have difficulty explaining away” requires that orders to call up the National Guard “be issued through the governors, which is obviously not happening here,” said Elizabeth Goitein, the senior director of the Brennan Center’s Liberty and National Security Program.

Less black and white, she said, is what happens “if the president tries to exercise the authority provided by that law to federalize the National Guard and the governor refuses to issue the orders.”

As the governor, Newsom is the commander in chief of the California National Guard. He said Monday that Trump “bypassed” his approval to take over a unit of the guard.

Newsom wrote to Hegseth on Sunday, asking him to rescind the troop deployment. The letter said the mobilization was “a serious breach of state sovereignty that seems intentionally designed to inflame the situation, while simultaneously depriving the state from deploying these personnel and resources where they are truly required.”

Newsom has warned that the executive order that Trump signed applies to other states as well as to California, which will “allow him to go into any state and do the same thing.”

Legal experts said the statute that the White House used to justify the National Guard mobilization is usually invoked in concert with the Insurrection Act of 1807, a wide-reaching law that gives presidents the emergency power to call up the military in the United States if they believe the situation warrants it.

Goitein said presidents generally invoke the Insurrection Act, then use the statute that Trump cited as the “call-up authority” to actually mobilize the military. How the law stands on its own, she said, “is one of the legal questions that have not come up before in the courts.”

The Insurrection Act has been invoked 30 times in the history of the country, and Trump has not invoked it in Los Angeles. It was last invoked for use in California in 1992, when then-Gov. Pete Wilson asked President George H.W. Bush to federalize the National Guard in the wake of the Rodney King verdict.

The last time a president sent the National Guard into a state without a request from the governor was six decades ago, when President Lyndon B. Johnson mobilized troops in Alabama to defend civil rights demonstrators and enforce a federal court order in 1965.

Bonta’s office said a president has only invoked the specific statute that Trump is using once before, when President Nixon mobilized the National Guard to deliver the mail during a U.S. Postal Service strike in 1970.

The argument that Trump has violated the 10th Amendment is a clever subversion of a line of thinking that has traditionally been backed by conservative judges, said Erwin Chemerinsky, the dean of the UC Berkeley School of Law.

The 10th Amendment says that the federal government only has the powers specifically assigned by the Constitution, and other powers are controlled by the states.

“The state has a strong argument that ... by nationalizing the state guard, that Trump is commandeering the state,” Chemerinksy said.

He said the Supreme Court has ruled on the 10th Amendment only a handful of times in recent decades, including saying that Congress couldn’t require states to accept federal mandates related to sports betting, background checks for guns and radioactive waste disposal.

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Times staff writer Seema Mehta contributed to this report.

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