I think the more moderate Democrats were scared by Bernie and AOC and looked quickly for the alternative that would head him off, in both cases. They might have preferred another candidate, but they were driven to find someone who could beat Bernie. After SC, that was clearlyJoe.
I think you get it at the end, here.
More than the DNC railroading Biden this go-around, it was the black voters in SC. That was the "wait and see" moment of the Dem primary season. It could've ended Biden's campaign there, but that voting block (I guess) didn't trust Bernie and didn't want to vote for a white unknown or woman. It's a really interesting state to look at, actually. Tom Steyer got more votes than Klobuchar and Warren combined. The South reeeeeally doesn't believe a woman can be the president.
So for every 10 non-Biden voters, 4 voted for Bernie, 1 each for Steyer, Mayor Pete, Klobuchar/Warren, and 2 for others.
Biden had just 5 fewer % than Obama in '08, in a relatively heavy black voting group, with Bernie getting 5% less than Hillary did in '08.
I don't think it's a stretch to say that voting block was okay with an unknown black candidate, but felt more comfortable voting for a familiar white guy in 2020. It bothered me at the time, but it is what it is.
And on an aside, if republicans stopped mentioning her all the time, AOC would be a relative unknown. They treat her like the Dems treat Trump - bordering on obsession. She was a surprise winner of her district and was part of a minor documentary, but she's not some big, scary thing. I find it odd that she's the one they're demonizing. She's so far down the Democratic totem pole.
Another aside - I see conservative colleagues posting being in favor of term limits so that horrible people like Nancy Pelosi can't stay in power for forever. It made me do a little research. She's been around a long time, sure, but she's only 10th in seniority in the House. Guess what party the 4 longest-tenured members are? Yup, Republicans. Ugh. The perpetual misleading is something I could really do without, all-around.