Section 1385 of title 18 (commonly known as the “Posse Comitatus Act”) prohibits the use of the Armed Forces as a posse comitatus to execute the laws except in cases and under circumstances expressly authorized by the Constitution or Act of Congress.

Enacted in 1878, the Posse Comitatus Act was expressly intended to prevent United States Marshals, on their own initiative, from calling on the Army for assistance in enforcing Federal law.

The Posse Comitatus Act has served the Nation well in limiting the use of the Armed Forces to enforce the law.

Nevertheless, by its express terms, the Posse Comitatus Act is not a complete barrier to the use of the Armed Forces for a range of domestic purposes, including law enforcement functions, when the use of the Armed Forces is authorized by Act of Congress or the President determines that the use of the Armed Forces is required to fulfill the President’s obligations under the Constitution to respond promptly in time of war, insurrection, or other serious emergency.

Existing laws, including chapter 13 of title 10 (commonly known as the “Insurrection Act”), and the Robert T. Stafford Disaster Relief and Emergency Assistance Act (42 U.S.C. 5121 et seq.), grant the President broad powers that may be invoked in the event of domestic emergencies, including an attack against the Nation using weapons of mass destruction, and these laws specifically authorize the President to use the Armed Forces to help restore public order.