First, he has failed to generate nearly any interest, let alone meaningful support, among young people in the presidential primaries. Second, he has consistently lost the Latino vote. And third, he suffers from a well-documented enthusiasm gap that could undermine his candidacy in the same way that Hillary Clinton failed to generate voter excitement, resulting in a drop in voter turnout among key constituencies, particularly African-Americans, whose diminished motivation and engagement resulted in the collapse of the Democratic “Blue Wall” states of Wisconsin, Michigan and Pennsylvania.

Mr. Biden’s minuscule levels of support among voters 18 to 29 — the electoral engine of Bernie Sanders’s campaign — has been alarming. In Michigan, a state he won handily over Mr. Sanders, Mr. Biden still secured only 19 percent of the youth vote. Even in South Carolina, the place that transformed the Biden candidacy, he still lost the under-30 vote to Mr. Sanders by 17 points, a margin that was twice as bad as Mrs. Clinton’s 2016 deficit against the same opponent in the same state.

Of note — and what should be of great concern to the Biden team — is that this weakness with young voters transcends racial lines.