You think the party elects presidents? It doesn't. People do, not politicians or parties. Your myopic view is what's wrong with American elections, particularly Democrats: the idea that a party can win by virtue of appeal to the machine.

Bernie would have won in 2016 if HRC, Wasserman-Schultz, Donna Brasil, and the DNC hadn't subverted his nomination. Again in 2020 if the DNC, Kamala, and the other candidates hadn't dropped out in favor of Biden against Sanders.

The idea that any candidate is owed the presidency is fucked. So is your misunderstanding of the problem.