Huh? The only vote Sanders won in SC: 18-29 year olds, made up just 11% of the electorate while voters 45+ were 2/3. Biden won them 3/1, black voters (56% of the vote) 4/1 and even white voters by 10%. Savaging Biden with no strategy to COURT black voters would have backfired. https://twitter.com/politico/status/1248781580480516100

Here are the demos from the exit polls, just to show my work: https://www.washingtonpost.com/graphics/politics/exit-polls-2020-south-carolina-primary/

If you want to read a really solid analysis of what went wrong for the Sanders campaign, I highly recommend this one from @voxdotcom. https://www.vox.com/policy-and-politics/2020/4/10/21214970/bernie-sanders-2020-lost-class-socialism

To summarize: the Sanders team never developed a strategy to court the majority of black voters, who are self-identified Democrats, and w/o a woman as his main challenger, his socialist pitch failed to move white working class voters out of their conservative, Republican lean.