A better explanation is that he simply did not have great appeal to traditionally Democratic voters in working-class, less liberal communities, regardless of race. It’s likely that Mr. Obama did especially poorly among white Southerners and Appalachians. His weak showing among Hispanics, however, suggests that much of Mr. Obama’s weakness among white Southerners and Appalachians was attributable to non-racial demographic characteristics, like the low level of educational attainment and Democratic voting tradition common to both groups.

In Texas, for instance, Mr. Obama’s worst counties weren’t white, conservative, Southern counties, but heavily Hispanic counties along the Mexican border. His worst was Starr County, where Mrs. Clinton won by a margin of 83 to 16 in a place where Hispanics represent 96 percent of the population.

Appalachian and Hispanic voters might seem very different, but they’re similar in crucial respects for a Democratic primary. The combination of low educational attainment and a strong Democratic tradition was a perfect combination for Mrs. Clinton. In well-educated areas, liberalism prevails and Democrats are liberal; in less educated areas where Republicans do well, conservatives prevail but most conservatives vote Republican; in the less educated but Democratic areas, whether along the Rio Grande or in the Appalachian region, there are many conservative Democrats.

To become a serious challenger to Mrs. Clinton, Mr. Sanders will need to do a lot better among less liberal and less educated Democratic voting blocs, whether white, black or Hispanic. Whether he does it by faring well in eastern Kentucky, along the Rio Grande or in Selma, Ala., is beside the point.