It's not that Biden doesn't support progressive ideals. It's just that he knows what is possible and what is totally unrealistic.
I am not going to argue with your main thesis, not because I disagree, but I just don't see what would practically come out of it. However, this comment, I'd like to point out doesn't quite match to established legislation or policy positions. Maybe it mostly does. Maybe.
But let me ask you.
What drove Biden to WRITE the busing law in the '70s? You are arguing that he is a progressive realist. How does being a progressive realist lead one to proactively write something like that?
Later on in the 90s, when it was popular for Democrats to call themselves conservatives and promote a balanced budget above anything else, this is what he did. He said "no sacred cows." He rhetorically went after the liberals in his party, i.e. the vast majority. How does this support your thesis that he's a progressive realist? Or were his actions on his own behalf for his own political survival? and the whole progressive realist thing takes a backseat to this?
In the 2000s, the Bankruptcy bill...…….? Again, this is something he WROTE. There were versions that the vast majority of liberals were against. Elizabeth Warren was always against every single version. It wasn't good for poor people. How does writing the bankruptcy bill support your thesis that he's a progressive realist?
I have maintained and continue to maintain that the majority of Biden's positions have been centrist and left but some also to the right....that he can be a good ally but he cannot always be trusted. It's not about survival, but instead some mixture of what he knows is the right position on things--and seeking to make himself look unique for sake of political power with moderates, right-wingers, and corporations. Therefore, keeping an active left movement or other kind of populist pressure on him is in the best interest of Americans. This can be now Bernie Sanders whose policy positions have altered how other campaigns take their own positions on issues, it can be from documenting his response to nuanced policy questions in a debate and then holding him to those things later because that is in his self-interest, it can also be from pressuring not to leave the primary until he agrees to choose a progressive VP or make some other cabinet concession involving Elizabeth Warren....for example.
Giving him carte blanche control to do what he's always done ensures he moves too far right later.
Now, again, I do agree that Sanders ought to concede and I've said this in this thread and elsewhere. But I'd like you to explain Biden.