A federal judge in San Francisco seemed unconvinced after a three-day trial that the continued deployment of federalized members of California’s National Guard — who were originally deployed to Los Angeles in response to protests against President Donald Trump’s immigration agenda — is lawful.

If President Trump deploys troops to other American cities, experts say it would be a clear departure from founding principles and invite a legal challenge.

Trump’s comment about using the National Guard or military follows his dispatch of troops to Los Angeles in response to protests of ICE raids. His decision to federalize the guard was opposed by California Gov. Gavin Newsom and Los Angeles Mayor Karen Bass, who said that the show of federal force inflamed the situation.