"how did the Democratic party get so messed up?"

Really simple: the unions once played an important role, preventing the liberals from going too far off the deep end. And the unions stopped having meaningful influence.

Now unions aren't powerful enough to get taken seriously by the Democratic party, even though the liberal elite are still acting as if they expect that union to vote for the Democratic candidate, no matter what.

The problem is, unions tend to be pretty much aligned with what you might call 'mainstream America'. If they hate a candidate, it's a pretty safe bet everyone else will, too.

Without unions, liberals are on their own as far as figuring out what makes a 'good' candidate. That's why it's such a problem when they look down their noses at those less affluent than themselves. There's a problem here that isn't being recognized or adjusted for.

Yes, the Democratic party has always been this messed up. A loose coalition of groups with a precarious balance at best (there is something comical about anti-globalization protests: you get to see environmentalists and labor agreeing on something for a change).