The problem is Democrats and their boosters feel entitled to the latter group's votes without having to give them anything and rely on the bogeyman of Trump and the GOP to threaten them into going along with it.
And for the most part, people do.
But when Democrats themselves willfully do horrible things like materially supporting genocide, the "lesser evil" equation starts to break down in the minds of potential voters, especially when the party treats them with contempt for disagreeing.