What Is the Posse Comitatus Act
The Posse Comitatus Act is an 1878 federal law that makes it a crime to use the federal military to enforce the law against civilians, unless the Constitution or Congress expressly allows it. In plain terms, soldiers cannot act as police. They cannot make arrests, run searches, or control crowds on American streets.
The name comes from an old legal term, posse comitatus, “the power of the county.” It meant the civilians a sheriff could summon to help enforce the law. The 1878 Act made clear that soldiers were not part of that posse.
A criminal law that almost never sees a courtroom. For most of its history the Act has been enforced by political tradition, not prosecutions. That is why a 2025 court finding that it was broken stands out.
Key facts
- It bars soldiers from policing. 18 U.S.C. 1385 makes using the military “to execute the laws” a crime, up to two years.
- It passed in 1878 as Reconstruction ended (Brennan Center).
- It binds the National Guard only when the president federalizes it under Title 10 (CRS).
- A judge found the 2025 Los Angeles deployment broke it willfully. That ruling is on hold during the appeal (Clearinghouse).
- Nearly 5,000 Guard troops patrolled Washington in July 2026 under rules the Act does not reach (NPR).
The Act has almost never been prosecuted, so its force comes from norms more than courtrooms. A president who sent troops into a city faced the political cost of appearing to turn the army on the country’s own people. The realistic risk of a conviction was close to zero.
What Military Policing Looked Like in Los Angeles
On July 7, 2025, about 80 soldiers from Task Force 51 parked Humvees and tactical vehicles around MacArthur Park in Los Angeles. They held two traffic control points on Wilshire Boulevard while federal agents marched through the park in an operation called Operation Excalibur. Its stated mission was “to demonstrate, through a show of presence,” the reach of federal law enforcement in the city, according to the government’s own planning slides.
The Los Angeles Police Department was to get two hours’ notice. The planners rated the risk of skipping the operation as low, because there were no high-value targets in the park. Agents met no resistance, and the troops never needed to protect anyone. Those facts come from the trial record in Newsom v. Trump.
Three days later, in Carpinteria, more than 80 miles from Los Angeles, troops and federal agents blocked Casitas Pass Road outside a cannabis farm. A video taken by the city’s vice mayor shows soldiers turning away a woman with a megaphone who was walking toward the blockade. The video became trial evidence.
Judge Charles Breyer read that record and ruled on September 2, 2025. Breyer wrote that the government had used troops “to set up protective perimeters and traffic blockades, engage in crowd control, and otherwise demonstrate a military presence in and around Los Angeles. In short, Defendants violated the Posse Comitatus Act.” The court found the violation willful.
Defendants violated the Posse Comitatus Act.
Judge Charles Breyer, Newsom v. Trump, September 2, 2025
The order barred troops in California from arrests, searches, security patrols, traffic control, crowd control, riot control, evidence collection, and interrogation. It did not order the troops out. The Ninth Circuit put the order on hold two days later, and in January 2026 it paused the appeal while related appeals played out. We found no later ruling on it as of September 2026.
Who Commands the Troops Decides Whether the Act Applies
The Act bites in only one band of command. Under a governor, the Guard can do police work because the Act does not apply. Under the president, federalized troops are barred, until the Insurrection Act lifts the bar again. The ladder below runs from state control to full federal control, and our National Guard explainer follows each 2025-26 deployment by the command it ran under.
Whether soldiers may do police work depends on who commands the troops
- State active duty Governor, state pays
The Guard serves its own state under state law. Many states let the governor use it to execute the laws.
- Title 32 duty Governor, federal government pays
Washington can request and fund the mission, but the governor keeps command, so the Act does not apply. Memphis, New Orleans and the out-of-state troops in Washington served this way.
- District of Columbia National Guard The president, always
The Justice Department says the D.C. Guard can serve in a militia status outside the Act, as it has in Washington since August 2025. The Brennan Center calls that a loophole.
- Federalized under Title 10 The president
Federalized Guard members are part of the federal military and bound by the Act. Los Angeles, Chicago, and Portland were federalized in 2025, and this is where the Los Angeles violation was found.
- Insurrection Act invoked The president, after a proclamation
Troops may enforce the law in the situations the Act defines. It is the main exception to the Posse Comitatus bar, last invoked in 1992.
| Step | Who commands | What the Posse Comitatus Act says |
|---|---|---|
| State active duty. The Guard serves its own state under state law. Many states let the governor use it to execute the laws. | Governor, state pays | Act does not apply, so policing is allowed |
| Title 32 duty. Washington can request and fund the mission, but the governor keeps command, so the Act does not apply. Memphis, New Orleans and the out-of-state troops in Washington served this way. | Governor, federal government pays | Act does not apply, so policing is allowed |
| District of Columbia National Guard. The Justice Department says the D.C. Guard can serve in a militia status outside the Act, as it has in Washington since August 2025. The Brennan Center calls that a loophole. | The president, always | Disputed in court |
| Federalized under Title 10. Federalized Guard members are part of the federal military and bound by the Act. Los Angeles, Chicago, and Portland were federalized in 2025, and this is where the Los Angeles violation was found. | The president | Act applies, so policing is barred |
| Insurrection Act invoked. Troops may enforce the law in the situations the Act defines. It is the main exception to the Posse Comitatus bar, last invoked in 1992. | The president, after a proclamation | Congress lifted the bar |
Sources: 18 U.S.C. 1385; Congressional Research Service R42659; Brennan Center, The Posse Comitatus Act, Explained (updated September 29, 2025); Newsom v. Trump (N.D. Cal. 2025).
The Supreme Court tied these rungs together in December 2025. In Trump v. Illinois, the president had federalized the Illinois Guard under 10 U.S.C. 12406(3), which applies when the president is “unable with the regular forces to execute the laws.” The Court read “regular forces” to mean the regular military. Because the Posse Comitatus Act bars the military from executing the laws, the Court reasoned, a president likely needs a real exception to the Act before federalizing the Guard on that ground.
The vote was 6-3, with Justice Kavanaugh concurring in the judgment, Justices Alito and Thomas dissenting, and Justice Gorsuch dissenting separately. The Insurrection Act explainer covers the Section 12406 fight in full, and our federalism explainer places it beside the grant fights between Washington and the states.
The statute names the Army, Navy, Marine Corps, Air Force, and Space Force. The Air Force came under it in 1956, and the Navy, Marine Corps, and Space Force were written in by the FY2022 defense bill, signed December 27, 2021. The Coast Guard is exempt because Congress gave it law-enforcement authority of its own.
What Soldiers Can and Cannot Do
The operative text is one sentence. It makes it a crime to use “any part of the Army, the Navy, the Marine Corps, the Air Force, or the Space Force as a posse comitatus or otherwise to execute the laws.” The line it draws runs between supporting civilian police, which is allowed, and doing police work, which is barred.
What federal troops may and may not do at home.
Source: CRS R42659; Brennan Center; Newsom v. Trump injunction (September 2, 2025)
Congress widened the “support” column in 1981, when it let the military lend equipment, intelligence, and logistics to civilian police, now codified at 10 U.S.C. 271-284. The Brennan Center counts 26 statutes that expressly let the military execute the law in some situation. The largest is the Insurrection Act, codified at 10 U.S.C. 251-255.
Where Each Deployment Stands in 2026
Courts stopped every federalized deployment, and the ones outside the Act kept going. Los Angeles, Chicago, and Portland ended by January 2026. Washington, Memphis and New Orleans, where the Act does not reach, continued past January. This table is current as of September 24, 2026.
Domestic military deployments since 2025, by legal authority and court status (as of September 24, 2026).
The Washington ruling was about statutes other than the Posse Comitatus Act. Judge Jia Cobb found two likely violations: using the D.C. Guard for crime deterrence without a request from city officials, and calling in other states’ Guards without authority under 32 U.S.C. 502. The appeals court panel said the president holds “a unique power” in the District because it is a federal district, not a state.
For the human aftermath of the immigration raids that set off the Los Angeles protests, see our brief.
Three Ways Troops Police Without Breaking the Act
The deployments that lasted used routes the Act does not cover. Each one is legal under current law, and each is contested.
Title 32 with a willing governor. The federal government can ask for a Guard mission and pay for it while the governor keeps command. The Brennan Center calls it a loophole, because those troops serve federal interests without the Act’s limits. More than 20 governors, plus Puerto Rico and the U.S. Virgin Islands, sent Guard members to Washington, NPR reported in July 2026.
The D.C. Guard’s militia status. The D.C. Guard always answers to the president, and the Justice Department has long held it can serve outside the Act. Guard members in Washington have been deputized as special police by the U.S. Marshals Service and carry firearms, according to the joint task force. They cannot make arrests, but they can hold someone until officers arrive.
Military zones at the border. Since 2025 the administration has turned federal borderland into six “national defense areas” in Arizona, California, New Mexico, and Texas. Troops there detain people for trespassing on military land. On August 14, 2026, the Justice Department’s Office of Legal Counsel said troops may also arrest people who leave a zone, citing the “military purpose” of a commander’s power to protect a base (CBS News). Courts have thrown out many of the trespass charges, the Christian Science Monitor reported.
How the Law Was Made and Narrowed
The arc runs from the Reconstruction-era bargain of 1878, through Little Rock in 1957, the drug-war opening of 1981, the Los Angeles riots of 1992, a short-lived expansion in 2006-2008, and the 2021 law that covered the sea services, to the two 2025 rulings.
- Congress passes the Act The Knott Amendment bars the Army from civilian law enforcement as Reconstruction ends.
- Little Rock exception Eisenhower uses the Insurrection Act to enforce school desegregation.
- Drug-war support roles open Congress lets the military lend equipment, intelligence, and logistics to police.
- Insurrection Act used for LA riots Its last invocation to date.
- Expansion passed, then repealed A 2006 law widens domestic deployment power; Congress repeals it in 2008.
- Navy, Marines, Space Force added The FY2022 defense bill writes them into the statute.
- Court finds the Act violated Judge Breyer rules the Los Angeles deployment broke the law willfully.
- Supreme Court blocks Chicago Trump v. Illinois ties Guard federalization to the Posse Comitatus bar.
Sources: Brennan Center; CRS; 18 U.S.C. 1385 statutory notes; Newsom v. Trump; Trump v. Illinois.
From the 1878 bargain to the 2025 rulings: 1878: Congress passes the Act (The Knott Amendment bars the Army from civilian law enforcement as Reconstruction ends.). 1957: Little Rock exception (Eisenhower uses the Insurrection Act to enforce school desegregation.). 1981: Drug-war support roles open (Congress lets the military lend equipment, intelligence, and logistics to police.). 1992: Insurrection Act used for LA riots (Its last invocation to date.). 2006-2008: Expansion passed, then repealed (A 2006 law widens domestic deployment power; Congress repeals it in 2008.). 2021: Navy, Marines, Space Force added (The FY2022 defense bill writes them into the statute.). Sept 2025: Court finds the Act violated (Judge Breyer rules the Los Angeles deployment broke the law willfully.). Dec 2025: Supreme Court blocks Chicago (Trump v. Illinois ties Guard federalization to the Posse Comitatus bar.).
1878: Congress passed the Act as the Knott Amendment, ending the Army’s role in civilian law enforcement in the former Confederacy. The Brennan Center notes it was meant to keep the military from interfering as white supremacists regained power in the South.
1957: President Eisenhower invoked the Insurrection Act to send the 101st Airborne to Little Rock and enforce a federal desegregation order.
1981: Congress opened drug-war support roles, letting the military assist civilian police with equipment, intelligence, and logistics. It was the first major erosion of the wall.
1992: President George H.W. Bush invoked the Insurrection Act during the Los Angeles riots, at California’s request. It has not been invoked since.
2006-2008: A 2006 defense law expanded the president’s power to deploy troops domestically. Congress repealed the expansion in 2008.
2021: The FY2022 National Defense Authorization Act, signed December 27, 2021, added the Navy, Marine Corps, and Space Force to the statute. The sea services had been covered only by Pentagon policy.
September 2025: Judge Breyer ruled the Los Angeles deployment willfully violated the Act, the first such finding in living memory.
December 2025: In Trump v. Illinois, the Supreme Court held the president likely could not federalize the Illinois Guard under Section 12406 without an exception to the Posse Comitatus Act.
Why Keeping Soldiers Out of Policing Matters
Civil-military separation is a liberty safeguard with roots older than the Act. The Brennan Center traces it to the Constitution’s split of military power between Congress and the president, and to the Third, Fourth, Fifth, and Sixth Amendments, written partly in reaction to British troops in the colonies. Soldiers are trained to defeat enemies. Police are trained, and legally bound, to protect the rights of the people they stop.
The 2025 record cuts both ways. Courts enforced the Act in Los Angeles, and the Supreme Court narrowed the Guard call-up power. Meanwhile the deployments outside the Act’s reach grew. Washington’s doubled to nearly 5,000 troops, and the border zones gained new arrest power.
How Congress Could Close the Gaps
Every route around the Act runs through a law Congress wrote, so Congress can narrow each one. The Brennan Center’s reform agenda lists five changes. Cut back the 26 statutes that allow military policing. Bring Title 32 Guard missions under the Act. Strike the statute’s nod to “constitutional” exceptions, which the Brennan Center says do not exist. Stop letting “indirect support” slip past the ban. Give people a remedy, such as throwing out evidence troops gathered or letting them sue.
Two bills in this Congress would close part of the gap, and both still sit in committee. The Supreme Court has already narrowed one route on its own.
Where the Limits on Domestic Deployments Stand
As of September 26, 2026
- Insurrection Act of 2025 (S. 2070, H.R. 4076) Proposal, in committee
Introduced in June 2025. It would end any Insurrection Act deployment after seven days unless Congress approves it. (source)
- National Guard Proper Use Act (H.R. 5604) Proposal, in committee
Introduced September 26, 2025. It would bar troops and Guard members from being ordered to enforce immigration law. (source)
- Guard call-up law (Section 12406) Blocked by a court, narrowed
In Trump v. Illinois on December 23, 2025, the Supreme Court read "regular forces" to mean the military, which kept the Chicago deployment blocked and means the president likely needs an exception to the Posse Comitatus Act first. (source)
Source: govinfo bill status; Supreme Court of the United States; Brennan Center for Justice
When Troops at Home Are Legitimate
The disagreement over military force at home is real, and serious people hold each side. Both sides agree the Act has genuine exceptions. The fight is over where legitimate use ends.
The administration’s case rests on protection and deference. It argued in Los Angeles that the president has inherent constitutional power to protect federal property and officers, a “protective power” the Justice Department also relies on at the border. It argues that protecting people and buildings is not executing the laws, and that courts should defer to a president’s judgment that an emergency exists.
The case for a strict line comes from the Brennan Center, Lawfare writers, and the courts that ruled in 2025. Judge Breyer found that the Los Angeles missions went far past protecting buildings, into blockades and crowd control with no specific threat. The Brennan Center argues the Act has no real constitutional exceptions and that its gaps for Title 32 and the D.C. Guard should close.
Some distinctions hold across both views. Disaster relief is not policing, and lending equipment is not making arrests. A governor commanding the Guard is not the president commanding it. The hard cases sit between those pairs, such as troops who stand at a checkpoint without making an arrest. Courts and Congress are still drawing that line.
Frequently Asked Questions
Can the president deploy the military on American soil?
Yes, but troops generally cannot do police work. The president can use them for support, disaster relief, and protecting federal property. Policing requires an express exception, and the main one is the Insurrection Act, last invoked in 1992.
Has the president violated the Posse Comitatus Act?
One federal court has said so. On September 2, 2025, Judge Charles Breyer ruled that the Los Angeles deployment willfully violated the Act. The Ninth Circuit put the order on hold, and the appeal was paused in January 2026.
What is the difference between Title 10 and Title 32?
Under Title 10 the president commands the Guard, and the Posse Comitatus Act applies. Under Title 32 the federal government pays and can request the mission, but the governor commands, so the Act does not apply.
Does the Posse Comitatus Act apply to the National Guard?
Only when the Guard is federalized under Title 10. On state active duty or in Title 32 status it answers to the governor, and the Act does not reach it. The D.C. Guard is a disputed case, because it always answers to the president.
What is the penalty for violating the Posse Comitatus Act?
A fine, up to two years in prison, or both. The Congressional Research Service counts only a handful of known prosecutions since 1878, and says compliance has mostly come from the military’s own restraint. In 2025 a federal court enforced it with an injunction in Los Angeles.
Is the Posse Comitatus Act the same as the Insurrection Act?
No. The Posse Comitatus Act bars the military from policing civilians. The Insurrection Act is the main exception that allows it in defined emergencies.
What You Can Do
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Ask your governor where they stand on Title 32 requests. A governor decides whether to accept a federally requested Guard mission and whether to send troops to another state. More than 20 governors sent troops to Washington. Ask yours, on the record, what they would do.
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Record military police work you see, from a safe distance. Note the time, the place, and any unit markings. A Carpinteria official’s video of soldiers at a roadblock became evidence in Newsom v. Trump. Our guide to your rights at protests covers filming safely.
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Ask your House member to back the National Guard Proper Use Act. H.R. 5604 would bar troops and Guard members from being ordered to enforce immigration law. It has been in the Armed Services Committee since September 2025.
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Learn the neighboring laws so you cannot be misled. Read the Insurrection Act explainer, the main exception to the Posse Comitatus bar, and the martial law explainer, which covers the military replacing civilian government.
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Write your senators and representative with the letter below. It asks them to cosponsor the Insurrection Act of 2025, which would end any deployment under that law after seven days unless Congress approves it.