The Posse Comitatus Act consists of just one sentence: “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.”
In practice, this means that members of the military who are subject to the law may not participate in civilian law enforcement unless doing so is expressly authorized by a statute or the Constitution.
Mr Trump could take a more far-reaching step by invoking the Insurrection Act of 1792, which would allow troops to directly participate in civilian law enforcement, for which there is little recent precedent.
Casting protests as an “insurrection” that requires the deployment of troops against US citizens would be riskier legal territory, one legal expert said, in part because mostly peaceful protests and minor incidents are not the sort of thing that the Insurrection Act were designed to address.
Posse Comitatus:
https://www.brennancenter.org/our-work/research-reports/posse-comitatus-act-explained
What does the Posse Comitatus Act say?
The Posse Comitatus Act consists of just one sentence: “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.”
In practice, this means that members of the military who are subject to the law may not participate in civilian law enforcement unless doing so is expressly authorized by a statute or the Constitution.
Found another possibility …
https://www.straitstimes.com/world/united-states/does-us-law-allow-trump-to-send-troops-to-quell-protests
So is there a case that marines don’t count then?
That’s a good question, the Marines are Navy adjacent, so I’m not sure how that works.
It’s weird that the act was updated to include the Air Force though since it was written in 1878.
The Air Force wasn’t officially founded until 1947. The Marines have been around since 1775.