When talking about, for example, the USSR, people seem to put some of the blame for their demise on the likes of Khruschev and Gorbachev. It seems like a major component of the downfall of the Soviet Union is the infiltration of the Communist Party by opportunists paving the way to a bourgeois counter-revolution.

My question is: can Communists do the same in order to help bring about a socialist revolution? Can principled Communists join, for example, the American Democrat or Republican parties and somehow weaken the state from within, until it can be smashed by a revolution?

If not, then why? And in the case that it’s not possible, then why is it possible the other way around?