To put Joe Biden’s South Carolina win in perspective, remind yourself of this. Ten or so days ago, he’d lost nearly all of a huge lead there and was nipping Bernie Sanders by very near the margin of error in some polls. I remember a 27-23 in there, with all the movement toward Sanders, him tightening up even the black vote. You could see the Sanders people on cable and Twitter carefully pre-gloating about the Palmetto Revolution.
Now, boom. Biden crushed the field. He won every county. In the exits, he won nearly every category, including African Americans by a thumping 61 to 17. Also, and this is interesting, turnout was very strong. It matched 2008, that year of peak Dem enthusiasm, which didn’t happen in Iowa or Nevada. It did happen in New Hampshire, but as David Wasserman noted, that appeared to be driven by Republicans voting (Republicans were eligible to vote in South Carolina, too; I don’t know how many did).
In other words, for the second time in four contests, we see high turnout correlated not with the candidate whose theory of victory is predicated on getting millions of new voters to the polls, but with the more mainstream Democrats, while the two states where Sanders won the popular vote had pretty anemic turnout.