Historic trial to test limits of military power in US law enforcement

The Posse Comitatus Act of 1878, a post-Reconstruction law that bars the use of military troops for domestic law enforcement, will head to a bench trial Monday for the first time in American history to determine if the Trump administration's federalization of the California National Guard and deployment of the Marines is legal.

Senior U.S. District Judge Charles R. Breyer will preside over the bench trial in San Francisco, which is scheduled to last three days. Newsom et al. v. Trump et al., 25-cv-04870 (N.D. Cal., filed June 9, 2025).

Sean J. Kealy, a clinical professor at Boston University School of Law, described the Posse Comitatus Act in a phone interview Tuesday as a "poorly written statute" but said its intent is clear: "You can't use the military as a law enforcement arm."

Breyer previously granted a temporary restraining order against President Donald Trump on June 12, ordering that control of the National Guard be restored to Gov. Gavin Newsom after he filed a lawsuit.

But a week later, a 9th U.S. Circuit Court of Appeals panel - comprised of Judges Mark J. Bennett, Eric D. Miller and Jennifer Sung - reversed Breyer.

The panel held that courts must show "high deference" to presidential decisions under 10 U.S.C. § 12406(3), which governs whether the National Guard can be federalized over a governor's objections to quell a rebellion, the danger of a rebellion, or if he is "unable with the regular order to execute the laws of the United States."

Neither Breyer nor the 9th Circuit panel took up the issue of the Posse Comitatus Act, however, and the San Francisco-based judge last month scheduled the three-day trial, which he combined with a preliminary injunction hearing.

Deputy Attorney General Jane E. Reilley, in a supplemental brief filed last week, argued that Trump's federalization of the National Guard and stationing of troops in and around Los Angeles violated the nation's founding principles.

"For nearly 60 days, the residents of Los Angeles and its surrounding regions have been subjected to a form of military occupation, with federal troops working alongside federal civilian law enforcement agents, often indistinguishable from each other, including while civilian law enforcement agents are engaged in operations in communities," she wrote.

"Even as Defendants acknowledge that the Posse Comitatus Act prohibits members of the military from engaging in civilian law enforcement activities, the military has done exactly that by impeding the free movement of civilians by forming perimeters and blockades on public roads and sidewalks, apprehending or detaining civilians, and participating in ICE raids across Southern California," Reilley added.

She cited a series of well-publicized examples of the National Guard's "active involvement" in civilian law enforcement operations, including the July 7 deployment of troops to MacArthur Park in Los Angeles and their involvement in a July 10 raid at cannabis farms in Camarillo.

But Justice Department attorney Garry D. Hartlieb, in a Monday response, wrote that the Posse Comitatus Act (PCA) dispute is limited and that California has no standing to sue.

"California cannot use a criminal statute with a mens rea requirement offensively in a civil action to prospectively enjoin the federal government's operations," he wrote. "Indeed, California has not identified a single case providing analogous relief in the nearly 150 years since the PCA's enactment, and the Government is unaware of any such case either."

Hartlieb cites 10 U.S.C. § 12406(3), on which the Trump administration prevailed at the 9th Circuit, to bolster the federal government's position. "The plain text of this provision and Ninth Circuit precedent establish that this language qualifies as an express authorization to conduct law enforcement for PCA purposes," he wrote.

The Posse Comitatus Act has rarely come up in federal litigation, often in motions by criminal defendants in discovery disputes that often have been won by the government.

Kealy, however, said the absence of precedent involving the law is largely because presidents rarely call up troops or bring in the military. It happened a few times in Southern states during the 1950s and 1960s when governors balked at allowing Black students to attend public schools or universities.

The outcome of the latest court case "will set a new precedent and give new contours to the Posse Comitatus Act," he said.