This is the truth, and it's more substantial than people realize.

A President, or nominee during campaign, is the de facto head of the party. If the party is registered voters, that's one thing, but that's about as substantive as me joining the Catholic church and saying the Pope doesn't speak for all Catholics. All the Cardinals and Nuns and Priests and so forth - they fall in line, or they're out. A parishioner is the currency that props up the institution, but they have no individual power, only meaningful in massive quantities. It's literally the same in politics. It's political suicide to go against the Party, and the Party is the candidate, because very very few have the personal influence to stay in office with the backing of the party.

Look at what they tried to do to Romney. He was literally the previous nominee and look what they tried to do to him. Not everybody is literally the previous nominee for President and the most famous Mormon in the world serving as a Senator from Utah. Not everybody can withstand that. And like to hear it or not, this is the same in both parties - functionally - Democrats have been faster to eat their own, like with Al Franken, but that's the nature of internal competition, nobody eats the President because as a matter of practical fact, the President is the party, at least until their day in the sun is done.

It's the reality.