South Carolina is usually won by an establishment Democrat, though a sufficiently impressive black candidate can win voters over. Hillary Clinton won 73% of the vote against Bernie in 2016, with Clyburn's endorsement. In the 2008 campaign, polling favored Hillary until Obama won other primaries and then won SC 55-27. Clyburn didn't officially endorse that year, but voted for Obama. This got him an angry phone call from Bill Clinton. Clyburn told him, "How could I ever look in the faces of our children and grandchildren had I not voted for Barack Obama?"
The last black candidate to win SC before Obama was Jesse Jackson in 1988. He supported Medicare for All, had Bernie's endorsement, and was the great left-wing predecessor to Bernie in my lifetime. Perhaps a candidate who shares Bernie's policies and can win SC will have to be black.
Clyburn is more typical of top Democrats who win elections for candidates like Biden than anyone at the DNC. He's highly placed in the House leadership, and has the unofficial responsibility of representing black community interests to powerful Democrats. When they use their power as he asks, they win favor with him, and that translates into presidential endorsements. This is how a lot of the DC economy of politics operates. It makes things hard for less powerful candidates who haven't built up a bank of favors with people like Clyburn.
Sanders' campaign messaging appears to have irritated Clyburn too: "I find it very interesting that someone is referring to African American voters in South Carolina as the establishment," Clyburn told The Daily Beast, referring to Sanders' claims that the Democratic establishment is coalescing around Biden in order to stop his campaign. "I don’t understand how that vote can be dismissed."
Broad anti-establishment messages resonate with many who recognize the party's past failures. But Clyburn heard these messages as an attack on him. He responded by throwing black support decisively behind Biden. It's a problem that I don't think the Sanders campaign recognized, and that progressives will have to solve in future primaries.
