Of course, Bernie Sanders shares the blame.

He has missed some opportunities to explain to black voters what sets his agenda apart, which has only reinforced the perception that he doesn’t appeal to them. And he has yet to deliver a comprehensive speech to clarify his views on the relationship between race and class. Since 2016, much of the media and some of his Democratic opponents have claimed that Mr. Sanders largely attracts white male voters — “Bernie Bros” — while dismissing the actual multiracial character of his base. The conclusion is that black voters are interested in “race” while Mr. Sanders and his followers are only interested in “class.”

Not only does this miss the ways that some African-Americans had gravitated toward Mr. Sanders, but it completely ignores his robust support among Latinos that have been at the heart of his primary victories out West. The basis of the multiracial support for Mr. Sanders is precisely because of the ways that race and class intersect in their lives, particularly African-Americans’.

Indeed, by the end of February, Mr. Sanders’s support among African-Americans had risen, a Reuters/Ipsos poll noted he had overtaken Joe Biden in support among African Americans. More-African Americans have supported his signature policy, Medicare for All, at 74 percent compared to 44 percent of white voters.

These are just some of the reasons that, for months, a majority of black voters under 35 have favored Bernie Sanders to Joe Biden. The jockeying of the black political class to line up behind the former mayor of New York and billionaire, Michael Bloomberg, is also evidence of a more significant political divide within African-American communities.

The South Carolina primary was a turning point for Joe Biden, where the endorsement from Representative James Clyburn proved decisive for 79 percent of African-Americans who cast their vote for Biden.

The overwhelming victory for Mr. Biden almost instantly changed the media narrative from Mr. Sanders’ nomination to lose, to Mr. Biden’s nomination to seize. The centrists consolidated around Joe Biden, including Pete Buttigieg and Amy Klobuchar, who quickly exited the race. Mr. Biden also benefited from the sudden collapse of the Bloomberg campaign.

These factors all set the stage for Bernie Sanders’s devastating setbacks on Super Tuesday and the primaries a week later. He did poorly among black voters, and the surge of new voters were white suburbanites for Biden, not the young and disaffected voters Mr. Sanders has always believed he could bring into the process.