The percentage of Democrats who say they are moderate has fallen from 44 to 35; the percentage of self-identified conservative Democrats has gone from 25 to 13 percent.

Well-educated whites, especially white women, are pushing the party decisively leftward. According to Gallup, the share of white Democrats calling themselves liberal on social issues has grown since 2001 from 39 to 61 percent. Because of this growth, white liberals are now roughly 40 percent of all Democratic voters.

While a substantial percentage of Democratic minorities identify as liberals, those percentages have not been growing at anywhere near the rate that they have for white Democrats, so blacks and Hispanics have not contributed significantly to the rising percentage of self-identified Democratic liberals. Over the past 17 years, for example, the percentage of black Democrats who identify themselves as liberals grew by a modest three percentage points, according to both Gallup and the Pew Research Center.

In fact, white liberals are well to the left of the black electorate on some racial issues.