A landmark trial kicked off on Monday over the use by Donald Trump’s administration of National Guard forces to support its deportation efforts and quell protests in Los Angeles, in a legal challenge to the U.S. president’s break from long-standing norms against deploying troops on American streets.

The three-day non-jury trial before San Francisco-based U.S. District Judge Charles Breyer will determine if the government violated a 19th century law that bars the military from civil law enforcement when Trump deployed the troops in June, as the state of California claims in its legal challenge.

“The factual question which the court must address is whether the military was used to enforce domestic law, and if so, whether there continues to be a threat that it could be done again,” Breyer said at the start of Monday’s court hearing.

Los Angeles experienced days of unrest and protests sparked by mass immigration raids at places where people gather to find work, like Home Depot stores, a garment factory and a warehouse.

The administration denies that troops were used in civil law enforcement and plans to show that they were protecting federal property and U.S. Immigration and Customs Enforcement agents.

Most of the Troops Are Gone

Many of the troops have been withdrawn, but California’s Attorney General Rob Bonta said on Monday that 300 National Guard members are still going on immigration raids and restricting civilian movements in the state. The Trump administration last week extended the activation of troops in the Los Angeles area through November 6, according to a court filing by Gavin Newsom, the state’s Democratic governor.

“The federal government deployed military troops to the streets of Los Angeles for the purposes of political theater and public intimidation,” Bonta said in a statement. “This dangerous move has no precedent in American history.”

California and Newsom have asked Breyer to prohibit the troops from directly participating in domestic law enforcement activities. They say the National Guard is accompanying ICE agents on raids and assisting in arrests, in violation of the Posse Comitatus Act of 1878 and other laws that forbid the U.S. military from taking part in civilian law enforcement.

The Republican president ordered 700 Marines and 4,000 National Guard troops to Los Angeles in June against Newsom’s wishes. California’s lawsuit ultimately seeks a ruling that would return its National Guard troops to state control and a declaration that Trump’s action was illegal.

A U.S. appeals court has allowed Trump to retain control of California’s National Guard during the legal challenge.

President Directly Controls National Guard in DC

The trial before Breyer will have limited impact, however, on Trump’s plan to deploy hundreds of National Guard troops to Washington as part of a crackdown on violent crime in the U.S. capital city despite statistics showing that violent crime there hit a 30-year low in 2024.

“I’m deploying the National Guard to help reestablish law, order and public safety in Washington, D.C.,” Trump said on Monday. “And they’re going to be allowed to do their job properly.”

Unlike in California and other states, where the governor typically decides when to activate Guard troops, the president directly controls the National Guard in Washington.

A ruling against the administration could restrict the actions of those troops and constrain Trump if he deploys such forces to police other American cities.

Trump said his efforts to fight crime will go beyond Washington and he has mentioned Chicago, Los Angeles, New York and Baltimore.

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(Reporting by Dietrich Knauth and Jack Queen in New York and Jan Wolfe in Washington; Editing by Tom Hals, Tom Hogue, Will Dunham and Andrea Ricci)