Regarding Waco, the FBI and ATF were using equipment loaned to them by the Army. Soldiers didn’t take part in the raid or standoff (so says Wiki, anyway, which agrees with my porous memory). I remember at some point coming across a federal law that not only allows but requires the US armed forces to provide such assistance to law enforcement; it’s not part of Posse Comitatus act, and I don’t know how to find it again. Can anyone help?