I'm not so sure about that. Our military forces have been training for some time to confront and defeat "domestic terrorists," which seems to mean anyone who disagrees with the government and is willing to speak openly about it.
Remember many lawmakers referring to aging Tea Party activists as extremists and terrorists?
Military personnel, by and large, do what they are told. Examples of this abound throughout history (Germany, Russisa, China, etc.) For those of you who would all me anti-military, that is simply untrue; I'm a proud 6-year veteran of the U.S. Navy.
I'm afraid that many in the military would follow orders to engage their own people. History suggests this to be true.