Like they say, you keep letting things pass and slide then that sets the stage for the final straw. That's the result of all the accumulation of bullshyt nobody dealt with over time when they had the opportunity to and now it's all blowing up in people's faces.
this has been the story of the democratic party for decades, from kennedy to carter, through clinton and obama, up to biden. they’ve largely skated by on performative gestures to progressive causes, papering over their complicity with empty platitudes and a well oiled public relations engine fueled by the mainstream media’s careful separation of the two parties within the controlled parameters of “debate” in our society.
the public has been conned into thinking the democrats are the “good guys,” which, as you noted, has allowed the crimes of both parties to accumulate over time.
the current flood of migrants from latin america is another crisis that can be attributed to policy that has been implemented by both parties since the end of ww2, plans that have been executed on behalf of corporations, resulting in a grotesquely impoverished region whose indigenous population has been consigned to almost slave-like conditions.
but, the public is a lot more informed, and many of them are waking up.