In recent weeks, President Donald Trump deployed National Guard troops to Washington, D.C., and — some months prior — to Los Angeles in an effort he says is aimed at reducing crime.
The president has also said he intends to send military personnel to Chicago, despite a California federal judge ruling last week that the administration’s deployment of troops violated federal law, specifically the Posse Comitatus Act.
What is the Posse Comitatus Act, and how does it apply to Trump’s deployment of the National Guard in California and Washington, D.C.?
Passed in 1878 after the end of Reconstruction — the post-Civil War era when federal troops enforced laws in the former Confederacy — the act prohibits the U.S. military from carrying out domestic law enforcement.
Dan Urman, director of the law and public policy minor at Northeastern University, who teaches courses on the Supreme Court, says the National Guard is often caught between state and federal authority. The guard generally reports to their respective state governors, “but if they get called into federal service, then the Posse Comitatus Act applies to them.”
“To work around this, presidents can ask governors to deploy their state’s National Guard members,” Urman says.
The law also prohibits the military from investigating local crimes.
In June, Trump ordered 2,000 National Guardsmen to be sent to California to protect Immigration and Customs Enforcement agents as they were performing raids to carry out what the White House called “basic deportation operations.” After the show of force on the West Coast, the president issued an executive order in August placing the local police under federal control in Washington, D.C.
Subsequently, more than 2,000 National Guard members from D.C. and other states were deployed into the nation’s capital to crack down on crime. Local crime statistics show that violent crime was down about 23% from August 12-26 compared to the previous two weeks. Federal officials reportedly made over 1,000 arrests.
More broadly, Urman says, the law “stands for the idea that we separate military and civilian affairs in the United States” — a principle that he says is fundamental to American values.
“Like all laws, there are, of course, exceptions,” Urman says. “The president can use the military to enforce federal laws and to suppress rebellions. As you can imagine, the definition of ‘rebellion’ is open to clashing interpretations.”
Federal district court Judge Charles Breyer said Trump’s recent deployment of the National Guard in Los Angeles violated the Posse Comitatus Act, writing that “there was no rebellion.” He noted that exceptions to the act are permitted only when expressly authorized by the Constitution or Congress — which had not occurred in this case.
Breyer notes that the government “systematically used armed soldiers and military vehicles to set up protective perimeters and traffic blockades, engage in crowd control, and otherwise demonstrate a military presence in and around Los Angeles.”
A White House spokesperson said last week that “President Trump is well within his lawful authority to deploy the National Guard in Washington, D.C,. to protect federal assets and assist law enforcement with specific tasks.”
