Why did Joe Biden win the Democratic primary and Bernie Sanders lose it?

Everyone has a theory: Sanders went too far left, or too far woke; he couldn’t expand his base, particularly into the black electorate; his surprise 2016 showing mostly owed to anti-Clintonism, and his insurgent campaign turned off loyal Democrats; meanwhile, Biden was an electoral powerhouse able to excite voters with his “moderate” agenda and historic ties to the party.

Accepting all this has meant crashing headlong into a series of inconvenient facts. Sanders’s leftward stances on issues like immigration supposedly lost him rural counties, but he had the best standing with rural voters, out of all Democrats. He supposedly alienated rank-and-file Democrats with his rhetoric, yet held sky-high favorability ratings among them throughout 2020. He failed to expand his base, but won nearly every demographic in Nevada, even moderates and conservatives, and led nationally among black voters on the eve of South Carolina.