The problem with Bernie was that while he had very vocal followers with a lot of passion, he didn't have a lot of them. His numbers stayed pretty constant as other candidates dropped out of the primary races. (I was, and am, a Sanders supporter.) It was much like Trump; Trump consistently pulled about 30% of the primary votes. Trump won the nomination because you needed a plurality to win the nomination, and too many candidates stayed in the race too long. In the Democratic races, other candidates dropped out earlier in the races, and their supporters went to Clinton and then Biden, rather than Sanders.

I agree with you that people on the left seem angry right now, but my fear is that they're angry with Biden, angry over Israel, angry over an economy that feels bad, and plan on taking their anger out on Biden rather than looking at this strategically. I'm a cis-, het-, middle-aged white male that likes guns. I look conservative as long as I keep my mouth shut. I know a whoooooole lot of people that don't have that luxury, and I'm scared for them.