The Democratic Party's fundamental problem is ultimately that the people they WANT to vote for them, are not going to vote for them, and the people who WOULD vote for them, want them to be significantly left of neoliberal Reaganism that got B.Clinton over.
And they alternate back and forth in every election since 2000, with "pretending to agree with our base" and "telling our base to shut up and get in line."
There's no fixing this without washing out the CONSERVATIVE LEADERSHIP of the party.