As President Donald Trump’s National Guard deployments to cities across the country have met with opposition from governors, city officials, and the courts, he has repeatedly threatened to invoke a law that would extend his power to deploy the military within the U.S.
Trump has floated the possibility that he could use the 19th-century law, the Insurrection Act, to bypass court rulings that restrict him from sending Guard troops to American cities over the objections of local and state officials.
“We have an Insurrection Act for a reason,” Trump told reporters in the Oval Office on Monday, calling it “a way to get around” pushback from officials and noting that he would invoke it “if it were necessary, but so far it hasn’t been necessary.” He described conditions that he said would prompt him to use the act, including “if people were being killed and courts were holding us up, or mayors or governors were holding us up.”
In a meeting with Canadian Prime Minister Mark Carney a day later, Trump was asked again if he would invoke the law. “It’s been invoked before,” he responded, before seeming to suggest he would consider using it in his federal crackdown in Chicago. “Chicago is a great city where there’s a lot of crime and if the governor can’t do the job, we’ll do that job.”
Read more: ‘Push Back Against Tyranny’: Chicago and Illinois Fight Trump’s Intensifying Crackdown
The comments come as Chicago and Illinois have sued in an effort to stop what they described as Trump’s “patently unlawful” deployment of hundreds of National Guard members to the city, and a federal judge has twice blocked similar efforts to send troops to Portland.
A separate federal judge ruled early in September that the deployment of Guard troops in Los Angeles this summer violated another 19th-century federal law.
That law, the 1878 Posse Comitatus Act, bars the President from using the military for law enforcement purposes within the U.S. But the Insurrection Act gives them more authority to deploy the troops domestically—in specific circumstances.
Here’s what to know about the act, and how it could be invoked.
What is the Insurrection Act?
The Insurrection Act, passed in 1807, allows the President to use the military as they deem “necessary” to enforce the law or suppress insurrection in the U.S. under certain conditions.
The text of the law says it can be invoked at the request of a state, or at the President’s own volition when they believe that “unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings.”
Read more: Can the President Activate a State’s National Guard?
But those conditions are vague, and largely left to interpretation, Chris Mirasola, a professor of law at The University of Houston Law Center, tells TIME.
“The statutes are variable, so they don’t provide us any definitions about what these terms mean,” Mirasola says.
He notes that it is a “common technique of statutory interpretation to use examples of past practice to give meaning to terms in the statute that are pretty ambiguous,” pointing to instances when the Insurrection Act has previously been used—and how they differ from the current situation.
When has it been invoked before?
The Insurrection Act has been invoked on multiple occasions over the years.
The last time was in 1992, when President George H.W. Bush deployed the National Guard, at the request of former California Gov. Pete Wilson, to suppress unrest in Los Angeles following the acquittal of four white police officers who were filmed beating Rodney King, an unarmed black man.
The act has also been invoked without the permission or request of a state. President Dwight Eisenhower, for instance, sent the 101st Airborne Division to Little Rock, Ark., in 1957 against the wishes of the governor to quell opposition to the integration of Central High School.
Mirasola tells TIME that when the law was used before, it was in response to “situations that are far more extreme than what we currently see in Portland or Chicago,” in which there were “riots and civil disturbances that are so large that federal functions literally cannot be exercised” and necessitated the intervention of the military.
The current conditions, he says, “just don’t rise to that level” seen in past uses of the act.
Read more: Why Trump Sending the National Guard to L.A. Is Different From Its Deployment There in 1992
Trump himself previously threatened to use the Insurrection Act during his first term in response to protests that swept the country after the killing of George Floyd by Minneapolis police in May 2020. While he did send troops to multiple cities that summer, he did not ultimately invoke the Insurrection Act, however.
The protests that have broken out in cities where Trump has deployed the Guard this year, such as Los Angeles and Chicago, have been notably smaller than the 2020 demonstrations, and have also been far more minor than the unrest that prompted the deployment of troops to Los Angeles in 1992.
Could Trump invoke it—and what would happen if he did?
Mirasola tells TIME that certain steps would need to be taken to invoke the Insurrection Act.
First, the President would have to issue a proclamation that “tells the putative rioters that they have to disperse,” he says. Then an Executive Order would need to be signed invoking the authority of the act.
These two steps, according to Mirasola, happen in quick succession, as when President Lyndon B. Johnson invoked the act to address unrest during the Civil Rights era.
If Trump did invoke the act, Mirasola says, his Administration would likely face litigation challenging his interpretation of the law and the conditions set forth in its original statutes.
“I expect that litigation is going to focus on whether the statutory requirements of the Act are met,” he says.
State and local officials have pushed back against Trump’s deployment of federal agents and troops to combat crime and quell protests in their cities as unnecessary. And those leaders, along with rights groups and the residents of areas where Trump has sent the National Guard—or threatened to—have raised alarms about his use of the military in U.S. cities, whether under the Insurrection Act or not.
Read more: Trump Signals Greater Use of Military in U.S. Cities, Warning of ‘War From Within’
Rachel Van Cleave, a professor at the McGeorge School of Law, tells TIME that Trump’s recent deployments of the Guard and his comments about invoking the Insurrection Act threaten states’ abilities to govern themselves, which are protected from federal encroachment under the Posse Comitatus Act and the 10th Amendment.
“It’s pretty remarkable sending federalized troops into a state over the objections of the state officials,” she says, calling it “an actual physical intrusion on a state’s sovereignty.”
Van Cleave also noted that Trump’s deployment of the Guard might detract from the needs of the states where troops are being sent from, as California argued when members of its Guard were sent to Los Angeles.
“Yes, I’d be concerned about that. We have lots of fires in California, and they’ve been telling us that the big one is coming again,” she says.
