There is precedent, though:
The GOP are psychopaths and the establishment Dems are crooks. The country and the world are facing urgent existential threats, and neither party is fit for the task of responding.
So, y'all need a new party, stat. And there are only two ways to get there: either destroy the Dems from outside (as the Republicans did to the Whigs), or gut and skin the party to take it over (as the TPer's did to the GOP).
If fascist arseholes can successfully stage a mutiny in the GOP, decent folks should be able to do the same with the Dems. Bernie based his campaign on the idea that this was possible; the establishment Dems are fighting full-throttle to prove him wrong.
Which is unsurprising, as their wealth, privilege and power are under threat. And the people involved been pre-selected by the political system to be biased heavily towards ambitious self-serving amorality.