US President Donald Trump recently claimed he has “unquestioned power” under the Insurrection Act to deploy National Guard troops to San Francisco. The Insurrection Act grants the President authority to deploy military forces domestically to suppress insurrection or rebellion. Dating to 1807, it represents a narrow exception to the Posse Comitatus Act‘s general prohibition against military involvement in civilian law enforcement.

This threat comes amid significant legal developments. Last month, US District Judge Charles Breyer ruled that the Trump administration’s Los Angeles deployment violated the Posse Comitatus Act, finding troops engaged in prohibited law enforcement activities including arrests, traffic control, and crowd control. This month, US District Judge Karin Immergut ruled that Trump lacked the authority to federalize National Guard troops and deploy them to Oregon. As similar deployments loom for San Francisco, understanding the Act’s legal framework, requirements, and limitations is critical.

What is the Insurrection Act and what authority does it grant the President?

The Insurrection Act comprises three primary provisions, each with distinct requirements:

Section 251 allows deployment when a state requests federal assistance against insurrection. This respects state sovereignty by requiring explicit invitation from state authorities.

Section 252 authorizes military use when “unlawful obstructions” make it “impracticable to enforce the laws of the United States” through ordinary judicial proceedings. This permits unilateral presidential action when federal law enforcement is systematically obstructed.

Section 253 permits deployment when insurrection or domestic violence “opposes or obstructs the execution of the laws” and deprives people of constitutional rights that state authorities cannot or will not protect. This was famously invoked during the Civil Rights era.

Once properly invoked, the Act grants authority to suppress insurrection, execute federal law, or protect constitutional rights. However, military forces cannot be used for general law enforcement, as this circumvents the Posse Comitatus Act’s fundamental prohibition.

Recent litigation clarifies that even deployed military forces remain subject to Posse Comitatus restrictions unless the Act is properly invoked. In State of California v. Trump, Judge Breyer found that National Guard troops in Los Angeles violated the Posse Comitatus Act by engaging in law enforcement—setting up traffic blockades, conducting crowd control, and assisting with raids—without meeting the Insurrection Act’s requirements.

What legal requirements must be met before the President can invoke the Insurrection Act?

Proclamation Requirement: Section 254 mandates that before using force under Sections 252 or 253, the President “shall, by proclamation, immediately order the insurgents to disperse and retire peaceably.” This provides notice, opportunity to comply, and creates a public record of justification.

Different Standards: Section 251 requires formal state request. Section 252 requires determining that unlawful obstructions make federal law enforcement “impracticable”—a high threshold beyond ordinary crime. Section 253 requires findings of insurrection or conspiracy that obstructs federal law and deprives constitutional rights that state authorities will not protect.

No Prior Approval Required: Unlike other military force uses, the Act does not require congressional or judicial approval. The President may invoke it unilaterally (except Section 251). However, courts can review whether statutory prerequisites were met and constitutional requirements satisfied.

Proving Necessity: The President must demonstrate conditions meet statutory thresholds. Courts increasingly scrutinize these assertions. Judge Breyer found regarding Los Angeles: “There were indeed protests… and some individuals engaged in violence. Yet there was no rebellion, nor was civilian law enforcement unable to respond.”

This is particularly relevant to San Francisco, where officials argue crime is reaching historic lows. In a statement, San Francisco Mayor Daniel Lurie said:

Crime in our city is down nearly 30%, car break-ins are at 22-year lows, homicides are at 70-year lows, and San Franciscans are feeling positive about the direction of our city once again. And we are going to continue working every single day to build on this progress and keep our city safe 365 days a year.

What are the constitutional limitations on invoking the Insurrection Act?

Under the Fourth Amendment, military personnel cannot conduct warrantless searches or seizures without probable cause. The Los Angeles deployment raised concerns when troops participated in raids and established checkpoints detaining individuals. Judge Breyer noted that “bystanders… and even federal officials… were unable to distinguish Task Force 51 troops from federal law enforcement agents.”

Under the First Amendment, deploying military forces in response to protests raises acute concerns. Supreme Court precedent protects peaceful assembly even when protests cause inconvenience. Military deployment can chill protected speech through intimidation. Ranking among the country’s bluest cities, with upwards of 80% of the city’s residents having voted for Trump’s Democratic opponent Kamala Harris in 2024, and having seen a large turnout in this weekend’s “No Kings” protest, the city could argue a federal troop deployment would stifle free speech.

The Tenth Amendment reserves police powers to states. Federal military intervention in areas traditionally managed by state and local government implicates core federalism principles. In the 1952 case Youngstown Sheet & Tube Co. v. Sawyer, the Supreme Court established that presidential power is at its “lowest ebb” when acting contrary to congressional will—precisely the situation when deploying troops for law enforcement contrary to Posse Comitatus.

Judge Breyer applied Youngstown, concluding the President cannot override explicit congressional restrictions absent clear constitutional authorization. The Constitution’s Calling Forth Clause gives Congress, not the President, authority to regulate domestic military deployment.

Judicial review could serve as another obstacle in the Trump Administration’s path. While courts grant deference in military matters, this isn’t absolute. In the 1932 case Sterling v. Constantin, the Supreme Court held that “whether or not [military discretion limits] have been overstepped in a particular case, are judicial questions.” Judge Breyer rejected political question arguments, holding that statutory compliance and Posse Comitatus violations are justiciable.

When has the Insurrection Act been invoked historically, and what precedents exist?

The Act has been invoked approximately 30 times.

Civil Rights Era: The Act’s most celebrated uses protected Black Americans’ constitutional rights. President Eisenhower deployed the 101st Airborne to protect the “Little Rock Nine” in 1957 after Arkansas’s governor blocked school desegregation. President Kennedy federalized National Guard forces when riots erupted over Black student James Meredith enrolling at the University of Mississippi in 1962. These established precedent for enforcing federal court orders and protecting constitutional rights against state interference.

Los Angeles Riots (1992): President George H.W. Bush deployed troops after the Rodney King verdict sparked widespread rioting. California Governor Pete Wilson formally requested assistance, meeting Section 251’s clearest criteria: genuine civil unrest overwhelming local authorities, state request, and deployment limited to restoring order.

Limited Case Law: Despite historical invocations, little case law interprets the Act’s requirements, as deployments were brief and/or rarely challenged.

Successful invocations responded to actual insurrection or violence overwhelming local authorities—not ordinary crime. Civil Rights deployments enforced federal court orders and clear constitutional rights. Most had state cooperation or occurred when states actively obstructed federal law. Deployments were temporary, withdrawing once emergencies ended. The San Francisco threat differs markedly. There is no insurrection, no documented inability of local law enforcement (crime is at historic lows), no obstructed federal court order, and no state request.

Conclusion

The Insurrection Act grants significant presidential authority, but this power is neither unlimited nor “unquestioned.” The Act requires genuine emergency conditions—insurrection, rebellion, or systematic federal law obstruction—not disagreement with local governance or ordinary crime.

Recent precedent establishes courts will scrutinize statutory compliance and Posse Comitatus violations. Judge Breyer’s September 2025 ruling demonstrates courts will enjoin unlawful deployments and examine factual assertions supporting intervention.

A San Francisco deployment would face substantial obstacles. The city’s low crime rates, absence of insurrection or federal law obstruction, and state and local opposition undermine any factual predicate for invoking the Act. Deployment would likely trigger immediate litigation with reasonable probability of injunctive relief—affirming that the Act represents a narrow exception to the fundamental principle that military forces should not serve as domestic law enforcement.