Progressives haven't won a lot of elections. When they hold over 50% of Democratic seats, then we can talk about the soul of the party. Now the fight is pretty one sided.
It takes ground work to win. Folks to man the phone banks and door knockers. So far I've seen a lot of progressive rallies, but those folks are not always showing up on election day. Old folks vote. Old folks are more conservative.
How 45 won was he talked about the problems of working class whites. No one had done that in a really long time. Even the ones who knew he was full of shit, said, "but he is talking about us."
The Democratic Party can remember what happened to Clinton when he was impeached. His numbers went through the roof. They want to avoid that happening to 45. They think it makes more sense to let him hoist on his own petard. I tend to agree.