Many Democrats resent their own elites. There is a quiet tension between Democrats who wield cultural power and those who don’t. The former are active on social media, and clobber the latter — people who say or write the “wrong” thing.

The non-elites tend to feel judged and looked down on by the self-appointed savior class. “Politically correct” has become the phrase people use to define those who use cultural power to enforce ideological conformity. Seventy percent of Democrats who are not on social media say political correctness is a big problem. These are people silently but vehemently reacting against this social reign of terror. Biden communicates affection, not judgment, acceptance, not expulsion.

Have a better theory of social change. Sanders and Warren imagine they can rally movements of progressive supermajorities to transform American politics. The reality is that if they are elected we’ll be stuck with the same 42 percent-to-42 percent stagnant political war we have now.

Biden starts with the understanding that we are a closely divided nation. He understands the elemental fact that if you want to pass laws you have to go through Congress. As Damon Linker pointed out recently in The Week, Biden’s argument is that a center-left congressional coalition is the best we can do under present circumstances. That’s a more realistic theory of change. A beloved legislator like Biden is more likely to transform the political landscape than a down-the-line progressive.