Good question. If you have two parties ostensibly desiring office, and both will commit genocide, you punish the one that is ostensibly relying on you as their base until they stop the genocide. It’s a game of chicken with that party. And the Democrats lost that game. They thought “we will still get what we want even though we are genocides” and they didn’t.
So now. They will have to stop being genociders if they want to win next time. It would have been 4 years of genocide either way, but now the people have shown that if you want to win next time, you need to not be genociders.
Wow. The two party system has you so fucked that you imagine if the Ds disintegrate that the only replacement would be the Republicans. Read history, I beg you. The Ds will disintegrate over the next decade and they will be replaced by a better stronger party that takes their place.