Amicus Briefs Published September 9, 2025

Newsom v. Trump — Federalization of the National Guard (CA)

United States Court of Appeals for the Ninth Circuit

Issue Areas
  • Rule of Law
In This Resource
Summary

Amid protests in response to the Trump administration’s immigration policies and enforcement in June 2025, the president deployed California’s National Guard without the consent of Gov. Gavin Newsom. Among the 4,000 members of the military who were sent to the streets of Los Angeles were 700 active-duty Marines.

The governor is normally the commander in chief of a state’s National Guard. Not only is federalizing the National Guard a highly unusual move, but administration officials did not consult with California leaders before doing so. The president even threatened to arrest Newsom if he interfered.

Newsom objected to the deployment, saying the National Guard should have remained under his control and should not have been used to assist the administration’s efforts to tamp down protests or help federal law enforcement officers conduct immigration activities throughout the region. The governor also emphasized that the National Guard members that Trump deployed were taken away from crucial emergency response efforts throughout California, including from the border.

On June 9, 2025, California sued the Trump administration in the U.S. District Court for the Northern District of California, arguing the deployment was an unconstitutional infringement on state authority and exceeded the president’s authority. Newsom cited the Posse Comitatus Act, an 1878 law that bars the use of the military against civilians. The district court sided with Newsom and temporarily returned control of the National Guard to him.

The Trump administration appealed to the U.S. Court of Appeals for the Ninth Circuit, which paused the district court’s decision while litigation proceeds. The three-judge panel held that the president was due significant deference, and that at least one provision of the statute used to federalize the National Guard had been satisfied. (This decision is currently being considered for review by a larger group of Ninth Circuit judges.)

Both Newsom and the Trump administration have filed their initial briefs on the merits before the appeals court after the district court’s decision.

Latest update

On Sept. 9, 2025, nearly a dozen retired senior military officers and Vet Voice Foundation, represented by States United, filed an amicus brief in support of California. Vet Voice Foundation is a nonpartisan, nonprofit organization that empowers veterans and military families to uphold democratic values.

The brief argues that the military should remain nonpartisan, rather than be deployed in highly politicized circumstances such as this; it should also only be used rarely in response to civilian disturbances. This federalization and deployment “should give any supporter of the military and military members pause,” and risks the reputation, integrity, and morale of the military, according to the brief.

“In a nation of law and order, not military rule, setting a precedent that allows the executive to deploy the military to any protest across the country will severely harm the military as a trusted and nonpartisan institution,” write the veterans.

The amicus brief was filed days after a federal judge found the administration’s use of the California National Guard for civilian law enforcement was illegal following a trial in separate proceedings. U.S. District Judge Charles Breyer said the administration was “creating a national police force with the president as its chief.”

There are still as many as 300 California National Guard members under control of the federal government. On Aug. 5, 2025, Defense Secretary Pete Hegseth extended the federalization of the California National Guard for 90 days, which is the subject of a separate legal challenge filed by Newsom.

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