The Democrats have captured "safe leftists" - folks who absolutely agree with leftist, collectivist, or communalist ideals, but whose conditioning makes them wary of pushing too hard in that direction.
The "progressive" Dems speak well to this audience, providing a "safe" leftism that is, in actuality, just a "liberal" form of the same supremacist ideas everyone is naturally abhorrent to.
Dems make supremacy safe.
They used to be the party of slave owners, after all.