Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army, the Navy, the Marine Corps, the Air Force, or the Space 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.
www.law.cornell.edu
There is the whole law, one flippin sentence. I mean where do you see exceptions explained? Under circumstances expressly authorized by the Constitution? What circumstances? There is no authorization, no claim to exemption, in any part of the Constitution. Has Congress authorized any of these actions? Why not?
Hell, it is comical really. Under normal circumstances, call up the National Guard, under state authority, Posse Comitatus doesn't even apply. But the president has to be asked, by the governor, in order to activate the guard under state authority. But federalize them, like he is doing in Illinois and headed for Chicago, against the governor's wishes, and suddenly, Posse Comitatus applies to federalized guard troops. That is what is stopping things in Portland.