There are few laws that President Trump mentions more frequently than the Insurrection Act.
The law, a 200-year-old constellation of statutes, grants emergency powers to compel active-duty soldiers to perform civilian police duties, something that would otherwise be prohibited by federal law.
Trump and his team have threatened to invoke it almost daily for weeks; the last time on Monday, after a journalist pressed the president on his increasing efforts to send federalized troops to Democratic-led cities.
“Insurrection Act… yeah, I mean, I could do that,” Trump said. “Many presidents have done it.”
About a third of American presidents have invoked the statutes at some point, but history also shows that the law has been used only in times of extraordinary crisis and political upheaval.
The Insurrection Act was Abraham Lincoln's sword against secessionists and Dwight D. Eisenhower's shield around the Little Rock Nine, the young black students who were the first to desegregate Arkansas schools.
Ulysses S. Grant invoked it more than a half-dozen times to thwart coups in statehouses, stop race massacres, and quell the Ku Klux Klan in its South Carolina cradle.
But just as often it has been used to crush labor strikes and strangle protest movements. The last time it was invoked, Secretary of Defense Pete Hegseth was in elementary school and most American soldiers were not yet born.
Now, many fear that Trump could turn to the law to quell opposition to his agenda.
“Democrats were fools not to amend the Insurrection Act in 2021,” said Kevin Carroll, a former senior adviser at the Department of Homeland Security during Trump's first term. “It gives the president almost unlimited power.”
It also excludes most judicial review.
“It can't even be questioned,” Trump boasted on Monday. “I don't have to go there yet, because I'm going to win on appeal.”
If that winning streak cools, as legal experts say it could soon, some fear the Insurrection Act will be the administration's next move.
“The Insurrection Act is written very broadly, but there is a history of even the executive branch interpreting it narrowly,” said John C. Dehn, an associate professor at Loyola University Chicago School of Law.
The president first floated using the Insurrection Act against protesters in the summer of 2020, but members of his Cabinet and military advisers blocked the move, as did efforts to use the National Guard to control immigration and the military to patrol the border.
“They have a real obsession with using the military on a national level,” Carroll said. “It's sinister.”
In his second term, Trump has relied on an obscure subsection of the U.S. code to send federalized troops to blue cities, claiming it confers many of the same powers as the Insurrection Act.
Federal judges disagreed. Since then, challenges to deployments in Los Angeles, Portland, Oregon, and Chicago have swamped appeals courts, with three West Coast cases before the U.S. Court of Appeals for the Ninth Circuit and one pending in the Seventh Circuit, which has jurisdiction over Illinois.
The result is a growing knot of litigation that, according to experts, will be up to the Supreme Court to resolve.
As of Wednesday, troops in Oregon and Illinois are activated but cannot deploy. The Oregon case is further complicated by the precedent in California, where federalized soldiers have patrolled the streets since June with the blessing of the Ninth Circuit. That ruling is scheduled to be heard again by the circuit on Oct. 22 and could be overturned.
Meanwhile, what California soldiers can legally do while federalized is also under review, meaning that even if Trump retains the authority to call up troops, he may not be able to use them.
Scholars are divided on how the Supreme Court could rule on any of those issues.
“At this point, no court… has expressed sympathy for these arguments, because they are very weak,” said Harold Hongju Koh, a professor at Yale Law School.
Koh mentioned that the high court's most conservative members, Clarence Thomas and Samuel A. Alito Jr., are unlikely to contradict the president's authority to invoke the Insurrection Act, but he said even some of Trump's appointees (Neil M. Gorsuch, Brett M. Kavanaugh and Amy Coney Barrett) could be skeptical, along with Chief Justice John G. Roberts Jr.
“I don't think Thomas and Alito are going to take on Trump, but I'm not sure Gorsuch, Kavanaugh, Barrett and Roberts can read this statute to give him [those] powers.”
The Insurrection Act sidesteps those fights almost entirely.
“It would change not only the legal situation, but it would fundamentally change the facts that we have on the ground, because what the military would be authorized to do would be much broader,” said Christopher Mirasola, an assistant professor at the University of Houston Law Center.
Congress created the Insurrection Act as a security measure in response to armed mobs attacking their neighbors and organized militias seeking to overthrow elected officials. But experts warn that the military is not trained to maintain law and order, and that the country has a strong tradition against internal deployments dating back to the Revolutionary War.
“Uniformed military leaders in general do not like to get involved in the issue of domestic law enforcement at all,” Carroll said. “The only similarities between the police and the army is that they have uniforms and weapons.”
Today, the commander in chief can invoke the law in response to a call for help from state leaders, as George HW Bush did to quell Rodney King's 1992 uprising in Los Angeles.
The statute can also be used to put a stop to elected officials who refuse to enforce the law, or mobs who make it impossible, something Eisenhower and John F. Kennedy Jr. did in defense of school integration.
Still, modern presidents have generally avoided using the Insurrection Act even in circumstances with strong legal justification. George W. Bush considered invoking the law after Hurricane Katrina created chaos in New Orleans, but ultimately declined out of fear it would escalate an already bitter power struggle between the state and federal governments.
“There are numerous internal Justice Department opinions in which attorneys general like Robert Kennedy or Nicholas Katzenbach said, 'We can't invoke the Insurrection Act because the courts are open,'” Koh said.
Despite its extraordinary power, Koh and other experts said the law has barriers that could make it more difficult for the president to invoke it in the face of naked cyclists or protesters in inflatable frog suits, whom federal forces have recently confronted in Portland.
“There are still legal requirements that must be met,” said Dehn, the Loyola professor. “The problem that the Trump administration would have in invoking [the law] is that in a very practical way, they are capable of arresting people who break the law and prosecuting people who break the law.”
Perhaps that is why Trump and his administration have not yet invoked the law.
“It reminds me of the lead-up to Jan. 6,” Carroll said. “It's a similar feeling that people have, the feeling that an illegal, immoral and reckless order is about to be given.”
He and others say an invocation of the Insurrection Act would move widespread concern about military surveillance of American streets into existential territory.
“If the Insurrection Act is invoked in bad faith to send federal troops to beat anti-ICE protesters, there should be a general strike in the United States,” Carroll said. “It's a real break-the-glass moment.”
At that time, the best defense may come from the military.
“If a really reckless and immoral order comes along… the 17-year-old generals should say no,” Carroll said. “They have to have guts to put their stars on the table.”
