I don't know about NEEDING a black candidate, but I have said since 2012 that going forward, Dems need to have at least one non-white person on the ticket.
It's not just "Muh identity politics"; the Democratic Party is built on minority support and the ticket should reflect that. Otherwise it's very easy for African-American/Latino voters to look at the ballot and say "None of these people represent me".
People vote on more than their gender and race. Working class white women voted Trump because Hillary wasn't doing sh**t for them.
Black people did turn out more for Obama then Clinton. Among whites, gender/race isn't the decider of identity politics as much as urban vs. rural or liberal vs. conservative. Harris seems to have the ability to
speak to minorities, unlike Warren or bernie, and she is a competent woman. She might be better if she waits until 2024/2028, though...
Ruben Gallego's district is pretty Hispanic(which implies that he appeals to people of Hispanic heritage). He clearly has some appeal there, and he seems to be heading the "don't trust trump" camp of democrats. Perhaps he could run.