Mr. Sanders’s problem runs a lot deeper than name recognition. A lot of these Democrats just aren’t consistently liberal, as the polling data suggests. It is not at all clear that a self-described socialist would fare well in the affluent, well-educated, socially liberal but fiscally moderate communities where Mr. Obama and even Bill Bradley excelled.

It is even harder to imagine how Mr. Sanders could replicate the strength among black voters that was essential to Mr. Obama’s success. Mr. Sanders has struggled to inch out of the single digits among nonwhite voters in national surveys.

As a result, there has been plenty of commentary about Mr. Sanders’s challenge among nonwhite voters.

But his problem with nonwhite voters is not properly understood as simply a problem of race. It’s primarily a problem with moderate and less educated Democrats, regardless of race, which happens to disproportionately affect his support among nonwhite voters.