Re: Why leave the door open to China?
The thought that the US military would be a part of a coup or engage in running the government shows a simplistic viewpoint of the world. While attended the Command and General Staff College at Fort Leavenworth, this very topic was discussed. All of the officers agreed that such a thing was not impractical but impossible. Simply speaking you couldn't get enough people to go along with such an idea.
The miliary has no interest in running anything or disagreeing with civilian control of the government. We are also quite aware that there are certain orders no military officer would obey from a civilian leadership.
As far as China being a threat. Not yet, but there abilities grow daily. They could cause us great difficulties in Asia if they were of a mind to. Try doing a bit more research next time.