I'm not sure if this is still the case, but when Nixon was president there was a special detachment of elite troops who were loyal to the president first and foremost. At a certain point in his mad administration, his aides recognised that Nixon was psychologically unfit to govern and they effectively took over his responsibilities. They ignored his orders (usually when he was drunk) and carried out their own orders based on Constitutional precedent and the law. The interesting fact is that the White House staff had to take into consideration how far away his elite troop barracks were (they were three miles from the White House) and how far away the 82nd Airborne were, because the 82nd are loyal to the Constitution. They were interested in this because, in the event Nixon called on his loyal troops to help him, the White House staff would have had to call in the 82nd Airborne to counter that move, which could have seen two elements of the US military in an armed standoff.
