If there is one American institution that reactionaries still respect, it is the military. As a result, if conspicuously apolitical military figures start telling the public in large numbers that Trump is an unfit commander in chief, that could be a major problem for him.
Of course, the other possible outcome is that Trump convinces his base that the military is just another component of the “deep state.” If that happens, the health of our political system will be on life support, because there will be no barriers left between 30 percent of the American public and fascism.