So as for Obama ordering the military to be willing to shoot Americans- He doesn't have to. Most of them are not adverse to the idea to begin with.
I have an uncle that was a student at Kent State when the shooting occured. He and several of his friends have a totally different story as to what started the shooting by the Guardsmen.
Ruby Ridge and Waco didn't have military involved. Ruby Ridge had FBI, ATF (now called BATFE) and US Marshalls. Waco had AFT and later the FBI joined in. So, this really isn't relevant to the military shooting civilians. Law Enforcement agencies (whether local/state police or Feds) kind of have to be willing to shoot civilians if warranted.
Shawn Nelson was shot by the police. However, since he stole US Army equipment, they ahd every right to go after him to get it back, and shoot him if he shot at them or otherwise jeapordized someone's life.
Bottom line, you don't need the military to collect the guns of the lawful gun owners, the cops and feds can do that. You need the military to be willing to kill US citizens in order to take become a dictator.
Also, once anyone in the military gives an order to kill citizens - they just violated their oath. Anyone in the military that just agrees to follow the unlawful order to kill citizens - they also just violated their oath.