Does he need the military when he has his paramilitary goon squads (TSA, IRS, etc.). If reports circulating on the Internet are even close to accurate, these organizations may have more small arms ammunition than the military itself. If the majority of the military is deployed overseas (or has been decimated), they won't be in a position to interfere.
It would be a brave soldier who would refuse to obey a lawful order from his commander. Your soldiers have fired on civilians in America before without question in the name of Homeland Security, as have the Police, The FBI first job was to hunt "undesirables" and were in existence long before the CIA or NSA. I refer to te New York riot in 1854, the "protection of Hawaii" in 1890, the "Communist agitators of the 1930s and 1950s.
I think you would find the engineering of an event of Mass Hysteria would be the easiest trigger down the slippery slope, especial with the 5th Admenment and your eggar media