Posse Comitatus Act – On the Shelf

In our ongoing attempt, as the people of this nation, to understand the current scene, I turn now to something that has been appearing in the news over the past several months: the Posse Comitatus Act. What is it? What is its history? Why is it important in today’s world?

The Posse Comitatus Act is a United States federal law, signed into existence on June 18, 1878, by President Rutherford B. Hayes. The act limits the powers of the federal government, and any other government entities, such as county sheriffs and justices of the peace, that are authorized to form a posse comitatus in the use of federal military personnel to execute the law within the United States.

The act was an amendment to the appropriations bill for the U.S. Army for 1879. It was passed as a response to, and subsequent prohibition of, the military occupation of the former Confederate states by the United States Army during the twelve years of Reconstruction (1865-1877). According to the United States Constitution, the maintenance of peace, conduct of orderly elections, and prosecution of unlawful actions are all responsibilities of the states — not of the federal government. When, in those former Confederate states, paramilitary groups sought to suppress (often through intimidation and violence) African-American political power, and return the South to predominantly white rule, the federal government sent in federal troops in support of African Americans. As Reconstruction went on, that support by the federal government waned. Following the 1876 presidential election, Congressional legislators from the former Confederate states returned to Washington, D.C., with the priority of prohibiting the federal government from reimposing control over their states. After President Hayes used federal troops to end the Great Railroad Strike of 1877, there was finally sufficient support for what became the Posse Comitatus Act.

The term “posse comitatus” is a somewhat strange term. It derives from the Latin, meaning “the ability to have a retinue or gang” — and is frequently just shortened to “posse”, the term with which we are more familiar. “Posse” originally meant the ability or power, but has carried the meaning of “the force” since medieval times. “Comitatus” is an abstract noun meaning “retinue”, but, again, carrying the meaning of a “commissioned body” since medieval times. In common law, posse comitatus is a group of people mobilized to suppress lawlessness, defend the people, or otherwise protect the place, property, and public welfare. The posse comitatus may be called by the conservator of the peace — typically a sheriff, chief, or other special/regional designee, such as a justice of the peace. There must be a lawful reason for a posse, which can never be used for lawlessness. The posse comitatus, as an English jurisprudentially defined doctrine, dates back to 9th century England.

Originally, the Posse Comitatus Act applied only to the United States Army. But, in 1956, an amendment to the act expanded its scope to the United States Air Force, and, in 2022, it was further expanded to include the United States Navy, Marine Corps, and Space Force. 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. Additionally, the United States Coast Guard is not covered by the act, primarily because it has a maritime law enforcement mission.

Why is the Posse Comitatus Act important to us today? It is because of how the federal government has recently been deploying federal forces, including National Guard troops and U.S. Marines, into cities to aid immigration efforts, as well as to address perceived criminal activity. However, there has been push-back to this effort. The 2025 lawsuit, Newsom v. Trump, raised constitutional and statutory challenges under the Posse Comitatus Act in response to the domestic deployment of those very troops in California. On September 2, 2025, federal judge Charles Breyer ruled that the federal deployment of the National Guard in California violated the act, and issued an injunction against it. We can expect for this debate to be further played out in other courts, and most probably, eventually, in the U.S. Supreme Court.

Library@Nite

A heads-up for those of you who like to plan ahead: the next Library@Nite (when the Downieville Library is open in the evening) will take place on Monday, October 13, 6:00 to 8:00 PM.