The latest test of President Donald Trump’s powers starts next week in California.

That’s when a federal judge will weigh whether the Trump administration violated a nearly 150-year-old law when it deployed thousands of National Guard and 700 active-duty Marines to Los Angeles this summer against the wishes of the state’s governor and the city’s mayor.

The bench trial will begin Monday in California, where Senior U.S. District Judge Charles Breyer will be asked to decide whether Trump had overstepped the Posse Comitatus Act of 1878, which forbids the U.S. military from acting as a domestic law enforcement arm except under the most extraordinary circumstances. The judge is also expected to hear arguments from both sides about the definition of a “rebellion.”

The stakes in the case are high, and not just for California: It will test the lengths to which Trump — or any future president — can use military force to quash unrest or sidestep local officials, as well as how they could plan to handle demonstrations or other crises in a given state.

The suit was brought by California Gov. Gavin Newsom and the state’s attorney general, Rob Bonta, who called the administration’s actions “an unmistakable step toward authoritarianism.”

Trump, the governor argued in his lawsuit, did not have the constitutional authority to send in troops or take over the state’s National Guard without his express consent. The administration had “manufactured [a] crisis,” the governor said in a June 9 statement.

“This is him intentionally causing chaos, terrorizing communities and endangering the principles of our great democracy,” Newsom said.

The case stems from Trump’s deployment of troops to respond to protests against immigration raids carried out in downtown Los Angeles’ Fashion District in June.

Protesters unsuccessfully attempted to stop those raids, with demonstrators gathering outside of a federal courthouse the night of June 6. Skirmishes broke out between protesters and police, and the courthouse was vandalised. Local police declared an unlawful assembly, and as rumours of more raids spread, other demonstrations cropped up, including one where a car was set on fire. The next evening, June 7, Trump issued a memo

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