As National Guard troops patrol the streets of Washington, D.C., President Trump has threatened to send soldiers to other cities across the country to help stop crime, but are they legally allowed to perform law enforcement duties? The answer depends on who deploys them.

"We're going to clean up our cities. We're going to clean them up, so they don't kill five people every weekend," Mr. Trump said when asked about his intention to send National Guard troops to cities like Chicago.

Troops in Washington, D.C., are tasked with securing monuments, community patrols and area beautification, among other duties. But using the National Guard to "clean up our cities" is lined with legal red tape.

"National guard troops under the command of the governor of a state can perform law enforcement duties within that state," Richard Painter, a law professor at the University of Minnesota, said. 

That means if Gov. Tim Walz were to activate the National Guard in Minnesota, like what happened during the George Floyd riots in 2020, they could be authorized to act as law enforcement, including making arrests. That's not exactly the case if the troops were activated by the president. 

"National Guard troops under the command of the President of the United States have a status similar to the U.S. military and are prohibited by federal law from engaging in law enforcement activities in the U.S.," said Painter before adding, "There are very few exceptions that would allow federal troops to be deployed for domestic law enforcement purposes."

One of those exceptions is to enforce a federal court order, which happened in 1957 when President Dwight Eisenhower sent troops to Arkansas to enforce desegregation of schools.

"Attempting to take over policing in, say, Minneapolis, that is simply beyond the power of the federal government," said Joseph Nunn, counsel in the Liberty and National Security program at the Brennan Center for Justice. 

The rules for what federal troops can and can't do are rooted in the Posse Comitatus Act from 1878.

"The Posse Comitatus Act bars the federal armed forces from participating in civilian law enforcement activities unless doing so has been expressly authorized by Congress," Nunn said.

If National Guard troops are sent to Chicago, Nunn said it would be a similar situation to what occurred earlier this summer in Los Angeles, when the president sent the Guard as well as several hundred marines to assist Immigration and Customs Enforcement operations as well as protect federal agents and property.

"If the government attempts to push beyond that, if the president actually tries to interfere in state and local law enforcement, you will absolutely see litigation," Nunn said. 

Litigation is what happened in California. Gov. Gavin Newsom sued in response to Mr. Trump's deployment of California's National Guard to quell protests against immigration enforcement.

Earlier this month, a federal judge in California ruled that Mr. Trump violated federal law with how troops were deployed in Los Angeles this summer.