President Trump threatened on Thursday to invoke the Insurrection Act for the first time in more than three decades and deploy the U.S. military to Minneapolis to “quickly put an end” to protests against Immigration and Customs Enforcement that have grown since an ICE agent shot and killed Renee Nicole Good last week.

“If the corrupt politicians of Minnesota don’t obey the law and stop the professional agitators and insurrectionists from attacking the Patriots of I.C.E., who are only trying to do their job, I will institute the INSURRECTION ACT, which many Presidents have done before me, and quickly put an end to the travesty that is taking place in that once great State,” Trump wrote on social media.

The president has mentioned the rarely used 1807 law before. Last October, he told reporters "we have an Insurrection Act for a reason," adding that “if people were being killed, and courts were holding us up, or governors or mayors were holding us up, sure, I’d do that” — meaning flood Democrat-led cities with federal troops to enforce his administration’s controversial mass deportation raids. Earlier, during Trump’s first term, aides reportedly drafted a proclamation to invoke the act as he fumed over the 2020 racial justice protests.

But Trump has never actually followed through on his Insurrection Act threats, and for good reason: Legal experts say that turning the U.S. military on today’s anti-ICE protesters would be unprecedented — and unpopular.

Here’s everything you need to know about the Insurrection Act as the president weighs whether to use it in Minneapolis.

What is the Insurrection Act?

The Insurrection Act is a group of statutes approved by Congress in the early 1800s to replace the “calling forth” act of 1792 — a post-Revolutionary War law that allowed the federalization of state militias in times of imminent invasion or insurrection. Together, they empower the president, under some conditions, to deploy the military on American soil.

When can the Insurrection Act be used?

Under the Posse Comitatus Act of 1878, the president is prohibited from using the military as a domestic police force.

But the Insurrection Act allows a few exceptions to this rule. According to the text of the law itself, the president can deploy the U.S. armed forces and the National Guard domestically in three specific situations:

• To “suppress” an insurrection against a state “upon the request of its legislature or of its governor if the legislature cannot be convened”

• To “suppress” an insurrection and “enforce” federal law when the insurrection — defined here as “unlawful obstructions, combinations, or assemblages, or rebellion” — otherwise makes enforcing those laws “impracticable”

• And to “suppress” an insurrection or “domestic violence, unlawful combination, or conspiracy” in any state if it deprives residents of a constitutional right and the state in question is “unable, fail[s], or refuse[s] to protect that right”

Minnesota Gov. Tim Walz opposes Trump’s immigration crackdown; he is unlikely to request federal troops. And no one is arguing that the state’s anti-ICE protesters are depriving residents of their civil rights. So Trump would presumably cite the second rationale — enforcing federal law — if he invoked the Insurrection Act there.

Before doing so, however, the president must first call for the “insurgents” to disperse, according to a Congressional Research Service report published in 2006. If stability isn’t restored, experts say Trump would then have unilateral power to declare that an insurrection is underway. The Insurrection Act does not define “insurrection,” “rebellion,” “domestic violence” or other key words, and an 1827 Supreme Court ruling gives the president exclusive authority to decide “whether the exigencies” that warrant invoking the act have been fulfilled.

“The vague and broad criteria for invoking the Act, combined with the lack of any provision for judicial or congressional review, render it ripe for abuse in ways that could directly threaten democracy,” according to the Brennan Center for Justice.

How has the Insurrection Act been used in the past?

The Brennan Center says the Insurrection Act has been invoked in response to 30 crises throughout American history. But in modern times it has never been used as Trump is proposing to use it: to unleash the military on the American people because they are protesting the president’s policies.

Instead, “presidents of both parties have been especially careful to use the military domestically only in contexts in which there was a clear factual predicate,” as Stephen Vladeck, a professor at Georgetown University Law Center, recently explained. In fact, “every modern use of the Insurrection Act has come either at a governor’s request or to expand civil rights protections over state objections,” according to Axios.

Dwight D. Eisenhower and John F. Kennedy used the power to enforce desegregation orders in the Jim Crow South. Ronald Reagan leaned on it in 1987 to end a hostage standoff at a federal prison — though he didn’t actually end up deploying troops. And George H.W. Bush was the last president to invoke the Insurrection Act when he did so at the request of the governor of California to quell the 1992 Los Angeles riots.

Notably, Trump did not invoke the Insurrection Act on Jan. 6, 2021, even though thousands of his supporters attacked the U.S. Capitol and tried to stop the lawful certification of Joe Biden’s election victory, injuring 174 police officers in the process.

Do the Minneapolis ICE protests qualify as an ‘insurrection’?

Some 3,000 federal immigration agents have flooded the Minneapolis area in recent weeks, angering residents and local officials. The Department of Homeland Security has described the massive deportation raid as “the largest DHS operation ever.”

Protests grew last week after an ICE agent identified by multiple media outlets as Jonathan Ross shot and killed Good, a 37-year-old mother of three who parked her car horizontally across the right lane of a one-way residential street in an apparent effort to impede ICE. Video footage taken from multiple camera angles and analyzed by the New York Times suggests that Good was turning and driving away from Ross as he opened fire.

Minneapolis officials said 30 protesters had been arrested over the weekend; one police officer had minor injuries after a “chunk of ice was thrown at them.”

Protesters and law enforcement officers clashed again in north Minneapolis on Wednesday evening after reports of escalating ICE apprehensions culminated in another shooting by a federal agent. According to the New York Times, protesters threw snowballs and fireworks; ICE agents fired canisters of gas and sprayed chemical agents. Two people were detained and later released. One unmarked vehicle with police lights was damaged.

Minnesota leaders have urged calm — even as some Washington, D.C., Republicans have claimed otherwise. “I can tell you that Minnesota is out of control,” House Speaker Mike Johnson told CNN. “You have local and state leaders who seem to be encouraging violence. The president’s frustrated about it, and so are we.”

So far, however, the public seems to disagree. According to a new Yahoo/YouGov poll, the number of Americans who say protests against the recent ICE raids have been mostly peaceful (34%) is higher than the number who say they’ve been mostly violent (27%). In contrast, Americans are more likely to see the raids themselves as “mostly violent” (42%) rather than “mostly peaceful” (19%).

How does the Insurrection Act differ from what Trump has already done?

In August, Trump invoked the Home Rule Act to bring the Washington, D.C., police department under federal control. He also deployed 800 National Guard members to the capital — which he can do without the consent of the local government (unlike in U.S. states, where the governor holds that authority).

Earlier, in June, Trump deployed nearly 5,000 National Guard members and U.S. Marines to Los Angeles after a new round of ICE workplace raids sparked protests marred by sporadic violence.

California Gov. Gavin Newsom swiftly sued the administration to end the mobilization, claiming that Trump was violating the Posse Comitatus Act. A federal judge agreed with Newsom after multiple appeals, and in a similar case, the U.S. Supreme Court eventually ordered Trump to relinquish control of the Illinois National Guard as well.

If Trump invokes the Insurrection Act, “the Supreme Court will no doubt have the last word” again, according to Vladeck. “The question is going to be whether the president can use a contrived crisis as a justification for sending troops into our cities,” Vladeck wrote in October. “In other words, the issue is going to come down to who decides the facts when it comes to domestic use of the military.”

Chart by Mike Bebernes