I think Sanders has been way too general and relying on "revolution". I see a lot more Warren switches.
Let me explain why I said that Biden's base (again, older black people) "just might" go elsewhere, and not "He's toast".
Black people are very transactional when it comes to working with other racial groups, particularly white people, out of necessity. Sometimes you have to work with a overtly racist person to get to some goal or other, and that includes Civil Rights workers. That's why I'm personally so fast to put clear-cut racists on ignore here - I have no need to deal with such a person here.
Am I appalled that Biden worked with some guy who said "Life, Liberty, and the Right to Pursue Dead (N-word)s"? No. He's a long-time congressman, I expected that. Am I shocked that he didn't like bussing? No, most people never really liked it, regardless of skin color. Black folks wanted good schools in their own neighborhoods, and yeah, Biden's right, to say that black people somehow need white people to learn is pretty racist on it's own. I keep saying, the problem with "separate but equal" was that nothing was actually equal.
I thought Harris was very effective, and showed that, like Hillary, she could get right under Dolt 45's skin and leave him raging for days. Biden was sloppy, and Mayor Pete - I've never been understood why he's such a media darling.
But the average black voter? Depends on whether they see Biden the way I did, or Harris as attacking Obama-Biden as a team. The guy who will really lose is Pete - that answer he gave for police shootings won't fly, and frankly, there's a lot of other ugliness that hasn't hit mainstream news that will absolutely sink him among black voters. But I already knew he was a dead man walking, so I didn't bother.
As far as white voters go? Kinda the same, except the Obama-Biden teamup isn't seen in such powerful terms.