ES, The use of federal troops for law enforcement is patently illegal in the United States. Posse comitatus ring a bell? However, in the past, right or wrong, we have given a pass to Officers who order their troops to fire on civilians if they were following orders from higher. We even celebrated one, and elevated him to a 5 star command, Gen. Douglas Macarthur.

ANY United States soldier who thinks that they are being given an illegal order has the right and the duty to question the order. Officers and NCO's are given classes in the law of land warfare, and are expected to enforce it. No troop does or should question every order, correctly (in most cases) assuming that their superior would not order them to commit an illegal act. When a superior gives a questionable order, it is questioned (Sir, would you please restate that? I'm not clear on what you meant?) and if the order is illegal, the NCO or senior leader present under the person issuing the order is supposed to relieve the person of duty. That is an extreme case, but that's the way the book plays out.