The Posse Comitatus Act

The Posse Comitatus Act is a United States federal law  signed on June 18, 1878, by President Rutherford B. Hayes. The purpose of the act – in concert with the Insurrection Act of 1807 – is to limit the powers of the federal government in using federal military personnel to enforce domestic policies within the United States. It was passed as an amendment to an army appropriation bill following the end of Reconstruction and was updated in 1956 and 1981.

The act specifically applies only to the United States Army and, as amended in 1956, the United States Air Force. Although the act does not explicitly mention the United States Navy and the United States Marine Corps, the Department of the Navy has prescribed regulations that are generally construed to give the act force with respect to those services as well. The act does not prevent the Army National Guard or the Air National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state's governor. The United States Coast Guard (under the Department of Homeland Security) and United States Space Force (under the Department of the Air Force) are not covered by the Posse Comitatus Act either, primarily because although both are armed services, they also have maritime and space law enforcement missions respectively.

The title of the act comes from the legal concept of posse comitatus, the authority under which a county sheriff, or other law officer, conscripts any able-bodied person to assist in keeping the peace.

So why threaten to use military if it is illegal? Remember the Patriot Act 2007???

"The President may employ the armed forces ... to ... restore public order and enforce the laws of the United States when, as a result of a natural disaster, epidemic, or other serious public health emergency, terrorist attack or incident, or other condition ... the President determines that ... domestic violence has occurred to such an extent that the constituted authorities of the State or possession are incapable of maintaining public order ... or [to] suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy if such ... a condition ... so hinders the execution of the laws ... that any part or class of its people is deprived of a right, privilege, immunity, or protection named in the Constitution and secured by law ... or opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws."

In 2008, these changes in the Insurrection Act of 1807 were repealed in their entirety, reverting to the previous wording of the Insurrection Act. It was originally written to limit presidential power as much as possible in the event of insurrection, rebellion, or lawlessness.