A three-day bench trial opened on Monday before U.S. District Judge Charles Breyer in San Francisco to decide whether former president Donald Trump violated the 1878 Posse Comitatus Act when he federalised roughly 4,000 California National Guard soldiers and 700 Marines and sent them to Los Angeles in June. California Governor Gavin Newsom and Attorney General Rob Bonta contend the deployment amounted to domestic law-enforcement, which the statute forbids, and are seeking an order returning the Guard to state control and barring further military involvement in policing. The troops were mobilised after protests erupted following federal immigration raids on 7 June. Although most forces have since departed, about 300 Guard members remain active and, according to state filings, continue to accompany Immigration and Customs Enforcement agents on workplace raids and form security perimeters. The Justice Department says the forces were used only to protect federal personnel and property and that Trump lawfully invoked Section 12406 of Title 10, which allows Guard activation when regular forces are insufficient to enforce federal law. Breyer said the central questions are whether the military was used to enforce domestic law and whether it may be used that way again. Witnesses expected to testify include senior Army and Homeland Security officials. A ruling—expected after the trial concludes on Wednesday—could shape Trump’s separate plan to deploy National Guard units to Washington, D.C., and limit future presidential attempts to send federal troops into U.S. cities.