The general purpose of the Insurrection Act is to limit presidential power, relying on state and local governments for initial response in the event of insurrection. The Posse Comitatus Act prohibits the use of the United States Army and Air Force (which has also been extended by executive direction to the Navy) for routine law enforcement. Actions taken under the Insurrection Act, as an "Act of Congress", are exempt from the Posse Comitatus Act.[1][2]
The Insurrection Act is brief. It allows the president, at the request of a state government, to federalize the National Guard and to use the remainder of the Armed Forces to suppress an insurrection against that state's government. It further allows for the president to do the same in a state without the explicit consent of a state's government if it becomes impracticable to enforce federal laws through ordinary proceedings or if states are unable to safeguard its inhabitants' civil rights.
The language of the act currently dates to 1871, when the Third Enforcement Act revised it to protect African Americans from attacks by the Ku Klux Klan.
The Insurrection Act has been invoked infrequently throughout American history, most recently following looting in the aftermath of Hurricane Hugo in 1989 and during the 1992 Los Angeles riots. [3][4]