The Posse Comitatus Act states that: Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both.
The Posse Comitatus Act, 18 U.S.C. § 1385, is perhaps the most tangible expression of an American tradition , born in England and developed in the early years of our nation, that rebels against military involvement in civilian affairs. The Declaration of Independence listed among our grievances against Great Britain that the King had "kept among us, in times of peace, Standing Armies without the consent of our legislatures," had "affected to render the Military independent of and superior to the civil power."
Despite Posse Comitatus, about 13,500 service members from the Army, Navy, Air Force, Marine Corps and Coast Guard will participate in the 57th Presidential Inauguration on Jan. 21, 2013, in ways ranging from logistical and ceremonial support to law enforcement.