A federal judge in San Francisco is weighing whether the Trump administration violated federal law by sending National Guard troops to accompany federal agents on immigration raids in Southern California.

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.