Federal law enforcement officers attempt to disperse demonstrators protesting Immigration and Customs Enforcement (ICE) activity outside the Bishop Henry Whipple Federal Building in St. Paul, Minnesota, on Thursday, January 15, 2026. | Victor J. Blue/Bloomberg via Getty ImagesThis story appeared in Today, Explained, a daily newsletter that helps you understand the most compelling news and stories of the day. Subscribe here.When I hear the word “insurrection,” I still think about January 6. It’s a strange twist of history — and also, probably, etymology — that this particular term is now finding new purchase in Minneapolis. On Thursday, President Donald Trump threatened to invoke the Insurrection Act, a seldom-used law some legal scholars have dubbed the country’s “most dangerous,” to crack down on protesters in the city. Those protesters have blocked traffic and hounded federal agents since an Immigration and Customs Enforcement officer killed Renee Good last week. Trump has made similar threats in the past, and it’s anyone’s guess if he’ll follow through. But even the suggestion of active-duty troops on the ground in a major US city is scary enough to justify a close look at the issue. In today’s edition, we answer the question: What is the Insurrection Act, exactly, and what will happen in Minneapolis if Trump invokes it? Plus: the MAGA media machine and microplastics.What is the Insurrection Act? The Insurrection Act is a centuries-old federal law that gives the president authority to deploy US troops inside the United States and use military force against Americans. Under normal circumstances, presidents can deploy troops almost anywhere they see fit, but those soldiers can’t perform civilian law-enforcement tasks, like making arrests or conducting searches, inside the US. The Insurrection Act creates a temporary exception. When can presidents invoke the Insurrection Act?The act allows the president to deploy troops in four situations: when a state government requests federal help, when a federal law or court order can’t be enforced through other means, and when violence deprives people of their constitutional rights or interferes with federal authority. That sounds pretty wide-ranging, and it is, but there are important limitations. Under the act, presidents can only deploy troops to protect federal property or enforce federal law, Lindsay Cohn, a US military expert at the Naval War College, told Vox in a 2020 interview. The federal government has also historically held that the Insurrection Act can only be used when “those engaging in violence are either acting with the approval of state authorities or have, like the Klan in the 1870s, taken over effective control of the area involved,” as the Justice Department put it in a key 1964 memo. But the law never actually defines “insurrection,” and legal scholars and organizations say that’s made it ripe for abuse. In 2022, one legal expert warned Congress that the Insurrection Act gives presidents “sole discretion, in most instances” to determine when and how it’s used. In an appearance on 60 Minutes last November, Trump claimed that the Insurrection Act allowed him to send the Army or Marines into US cities without judicial oversight or review. “Do you know that I could use that immediately, and no judge can even challenge you on that?” he asked. “But I haven’t chosen to do it because I haven’t felt we need it.”How have past presidents used the Insurrection Act?In a Thursday post on Truth Social, Trump argued that “many presidents” have invoked the Insurrection Act before. This is true; the act and related precursors have been invoked 30 times, mostly in the 1800s and early 1900s. George Washington used a precursor to the act to quash a (literal) rebellion over liquor taxes in 1794. Later presidents deployed troops to quell riots, crush frontier skirmishes, and force striking employees back to work. In the past century, presidents have used the Insurrection Act in only two situations: to defend the civil rights of Black Americans in states that actively opposed desegregation and to respond to requests for aid from state governments. The last time it was invoked was in 1992 during the Los Angeles riots that followed the acquittal of four police officers charged with beating Rodney King. The violent unrest killed 63 people, and California’s governor requested federal assistance. Trump, by contrast, has threatened to use soldiers to squash protests even over governors’ objections. And last year, he used a different federal law to deploy state National Guard troops to Portland, Chicago, and Los Angeles. How is invoking the Insurrection Act different from deploying the National Guard?The Insurrection Act lets Trump call up active-duty soldiers, not just National Guard members. And courts reviewing any deployments under the Insurrection Act would likely grant the president more latitude than they might otherwise, according to the Brennan Center for Justice. The Supreme Court ruled in December that it was illegal for Trump to use the National Guard to quash a small anti-ICE protest outside Chicago. In his opinion explaining the decision, however, Justice Brett Kavanaugh noted that Trump could still use the Insurrection Act to deploy regular troops. “One apparent ramification of the Court’s opinion is that it could cause the President to use the U. S. military more than the National Guard to protect federal personnel and property in the United States,” he wrote.Could troops arrest protesters or perform police work?In theory, yes. Invoking the Insurrection Act allows soldiers to function like civilian law enforcement. But the Act doesn’t override the Constitution or other federal statutes governing military use of force. Soldiers called up under the Insurrection Act still can’t search you without a warrant or your consent, for instance. And they’re required to use force as a last resort after all other methods have failed. It’s maybe worth noting that, according to the Minneapolis Star-Tribune, there are already more federal agents in the Twin Cities region than there are local police officers. Could the Insurrection Act be used for immigration enforcement?The Insurrection Act has never been used in immigration enforcement, and legal observers say that using the statute to deploy troops in that way would require a pretty willful misreading of the law. But Trump has repeatedly threatened to invoke the Insurrection Act not only to quell protests like those in Minneapolis but to secure “full operational control” of the US-Mexico border and carry out mass deportations. Whatever Trump’s ultimate goals, any invocation of the Insurrection Act would likely trigger a slew of lawsuits. Minnesota is already suing the federal government to end a surge of ICE agents in the state, arguing that it constitutes “a federal invasion” that has made Minnesota “less safe.”