Ever since Clinton beat Bush in 92, corporate Democrats have used that as "proof" that tacking hard to the center to try to pick up "moderate Republican" votes, and that conventional wisdom hasn't changed since.
But they never mention that Clinton won a rare three way race with a huge spoiler candidate taking votes from the Republican. That election should be taken as an outlier, it seems to me. Meanwhile the dems have been systematically abandoning their old base, thinking they have no choice.