A three-day bench trial opened Monday before U.S. District Judge Charles Breyer in San Francisco to determine whether President Donald Trump violated the 1878 Posse Comitatus Act and other federal limits when he federalized California’s National Guard and dispatched active-duty Marines to Los Angeles during June protests over immigration raids. California, led by Governor Gavin Newsom and Attorney General Rob Bonta, argues the deployment of roughly 4,000 Guard members and 700 Marines amounted to domestic policing and infringed on state sovereignty. State lawyers want the remaining 250–300 Guard troops returned to state control and a court order barring the federal government from using military forces in civilian law-enforcement roles. Justice Department attorneys say Trump acted lawfully under Title 10 §12406, which lets a president mobilize Guard units when regular forces cannot enforce federal law. They contend the troops merely protected federal property and Immigration and Customs Enforcement agents and did not arrest civilians. The legal question turns on whether the Los Angeles unrest qualified as a “rebellion” and whether soldiers crossed the line into policing. Early testimony featured Maj. Gen. Scott Sherman and Army Deputy Chief of Staff William Harrington, who acknowledged troops could set security perimeters if commanders felt threatened. The proceeding follows a Ninth Circuit ruling that temporarily let Trump retain control of the Guard, and it comes as the White House prepares additional National Guard deployments to Washington, D.C. Breyer’s decision, expected after this week’s hearings, could redefine the scope of presidential authority to put troops on U.S. streets.