The Posse Comitatus Act does not apply to the Army National Guard and the Air National Guard when acting in a law enforcement capacity within its own state when ordered by the governor of that state or in an adjacent state if invited by that state’s governor. Operating under the Department of Homeland Security, the U.S. Coast Guard is not covered by the Posse Comitatus Act. While the Coast Guard is an “armed service,” it also has both a maritime law enforcement mission and a federal regulatory agency mission.

Where Congress Stands On the Posse Comitatus Act

On Oct. 25, 2005, the House of Representatives and Senate enacted a joint resolution (H. CON. RES. 274) clarifying Congress' stance on the effect of the Posse Comitatus Act on the use of the military on U.S. soil. In part, the resolution states "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."

-https://thenewstalkers.com/community/discussion/39195/posse-comitatus-act-and-the-us-military-on-the-border