California Prepares Legal Challenge Over Potential Troop Deployment in San Francisco

California Governor Gavin Newsom has formally threatened legal action if former President Donald Trump proceeds with plans to deploy federalized National Guard troops to San Francisco. The state contends that such a deployment would infringe on California’s sovereignty and raise complex constitutional and federal-state questions. Newsom called the potential move a “direct assault on the rule of law.” Governor Newsom, along with California Attorney General Rob Bonta and San Francisco City Attorney David Chiu, has previously filed and joined lawsuits challenging federal use of the National Guard in the state under Title 10. The federal administration argues that deploying federal troops or federalized Guard units is permissible under certain statutes, particularly when federal property or operations are considered at risk. Legal precedent on this matter remains unsettled, creating what many analysts describe as a constitutional testing ground.

For instance, in June 2025, U.S. District Judge Charles Breyer ruled that the federalization of part of the California National Guard violated the Tenth Amendment and exceeded presidential statutory authority. The Ninth Circuit later stayed part of that ruling, leaving the federalization in effect while the appeal proceeds. California officials argue that sending troops into civilian areas would violate both the Posse Comitatus Act and longstanding federalism norms. Supporters of the governor emphasize that the litigation is about protecting state control over the Guard and preventing domestic deployment of federal forces without proper state consent. Critics counter that federal authority may be necessary when states cannot adequately safeguard federal interests.

As of now, Newsom’s office warns that any attempt to deploy troops in San Francisco without state approval will prompt immediate legal action. The dispute is expected to continue through the courts and may ultimately reach the Supreme Court. Beyond one city or one deployment, this confrontation raises broader questions about the balance between federal power and state sovereignty, trust, and accountability. For Californians and the nation, the outcome could set a lasting precedent for when, and how, federal force can be used on U.S. soil.