Last year, President Donald Trump threatened to invoke the Insurrection Act of 1807 for the first time in the 21st century.

Now, in the wake of last week’s Capitol Hill riots, the act is gaining renewed attention.

The federal law allows the president to deploy military troops within the nation to suppress civil disorder, insurrection and rebellion, among other threats. It allows the president to federalize the National Guard and use U.S. armed forces to combat insurrections against states and the federal government.

The law, signed by President Thomas Jefferson, has been invoked 14 times, most recently in 1992 by President George H.W. Bush in response to the Los Angeles County riots after the Rodney King verdict.

Four Los Angeles police officers were found not guilty of using excessive force during a violent arrest of King, a decision that sparked race riots and violence throughout the nation.

The law also can be used in cases in which citizens are being denied their lawful, constitutional rights, such as when President John F. Kennedy, on Sept. 10, 1963, used National Guard troops to enforce the desegregation of Alabama’s public schools.

The law was amended during the Hurricane Katrina crisis while George W. Bush was president. According to the University of Berkeley, Congress amended the act to include natural disasters, epidemics or other public health emergencies, as well as terrorist attacks. Bush did not invoke the law in his response to the devastating hurricane and its social and political aftermath.

In general, federal troops are not allowed to be used to enforce domestic policy within the boundaries of the U.S. The Posse Comitatus Act, which limits the use of the U.S. military for law enforcement within the U.S., was signed by President Rutherford B. Hayes in 1878, but the Insurrection Act allows that exception.

Last year, Trump threatened to call out the U.S. military in response to the deadly riots that resulted after George Floyd, an unarmed black suspect, died while in custody of the Minneapolis Police Department.

American cities erupted in violence and destruction in a seventh straight night of unrest, with several police officers shot or run over, amid threats from Trump to send in troops to “dominate the streets.”

Demonstrations also broke out in such places as Philadelphia, where hundreds of protesters spilled onto a highway in the heart of the city; and Nashville, where more than 60 National Guard members put down their riot shields at the request of peaceful protesters who had gathered in front of Tennessee’s Capitol to honor Floyd.

More than 5,600 people nationwide were arrested for stealing, blocking highways and breaking curfew, according to a count by The Associated Press.