this reads as if bernies fight is one of communism. communism would be to disregard/tear down the current system and not try to use it for change. yet bernie is trying to get elected in the system so he can change it but his supporters are complaining about someone else trying to get elected in the system to bring about the same change in a more detailed way.

if you are going to use the system then do it in the way that has the highest chance of success to achieve your goals.