He thinks he can direct the military to do anything he wants, because he has replaced a few people at the top with his toadies. His ringers are idiots if they believe career military men would follow illegal orders. Those high-ranking officers didn't get to their ranks by being stupid. The military has one of the most intense performance review infrastructures in our society. They know illegal orders when they see them. And they know they swore an oath of loyalty to the Constitution, not to Donnie.
I bet he could order ICBM launches right now and nothing would happen.