And if the President's military authority is absolute...?

...how is it that not one President in our 231 year history has never at least attempted to use it to overthrow the government and install himself as a dictator? Such action would obviously be completely unconstitutional, but if a President has thousands of heavily-armed soldiers backing him up, is there really anything that the few wimpy politicians in Congress could do about it? Or are the Supreme Court justices going to condemn him if there are a sea of tanks encircling the Court house? And a rogue president like this could ensure obedience from his generals by promising them well-paid positions after the coup is over with. I'm certainly not advocating it, but it just seems like it would be so EASY to pull off. Why is it that we have never had a crazy, power-hungry President try this?