Biden’s twin bases are black and moderate voters. Often, those are the same voters.

Former vice president Joe Biden takes a selfie with attendees during a primary-night rally in Columbia, S.C., on Feb. 29, 2020. (Sam Wolfe/Bloomberg)

Former vice president Joe Biden’s support in the Democratic presidential nominating contest has long been a function of his robust backing from two particular voting blocs: black Democrats and Democrats who self-identify as moderate.

Those groups have more overlap than you might realize.

Over the past two decades, the density of self-identified liberals in the Democratic Party has increased significantly. In 2018, Gallup polling indicated that liberals made up a majority of the party, although that faded slightly last year. Those shifts have not occurred uniformly across the demographic groups that make up the party, though. While white Democrats have seen a 20-point increase in identifying as liberals, according to Gallup relative to a 2001-to-2006 baseline, the increase among black Democrats has been only eight points. Among Hispanics, the increase was nine points.

While the Republican Party is largely conservative, the Democratic Party is still divided between liberal and moderate members. A majority of Democrats in the 2018 General Social Survey, conducted every two years by NORC at the University of Chicago, identify as moderate or “slightly liberal.” About a third identify as liberal or “extremely liberal.”

Again: This is self-identification, meaning that these identities don’t necessarily translate into stances on particular policy positions. It is, however, the same way in which party is identified in the polls that show Biden with strong primary support among moderates.

When we break out the ideological splits above by race, the difference between white non-Hispanic Democrats and Hispanic or black non-Hispanic Democrats is obvious. Sixty percent of black and Hispanic Democrats identify as moderate or slightly liberal. Nearly half of whites identify as liberal or extremely liberal.

According to the GSS data, nearly two-thirds of those identifying as liberal are white. Half of those identifying as slightly liberal are white, too. But blacks constitute a plurality of self-identified Democratic moderates.

In other words, the GSS data suggest that perhaps 16 percent of Democrats are black moderates or conservatives.

Take that with a grain of salt. The density of black Democrats in the GSS data is larger than in other polling, like Pew Research Center’s 2018 data suggesting that about a fifth of Democrats are black. It is, nonetheless, a significant chunk of Democratic voters.

We saw this in South Carolina on Saturday. In that primary, exit polling suggests that black, moderate voters were a central part of Biden’s support.

Group	Percent of electorate	Biden
White	40%	33
Black	56	61
Very liberal	19	42
Somewhat liberal	30	42
Moderates	50	54

The question for Biden moving forward is whether there are enough black and moderate voters in future contests to allow him to stay even with the delegate lead of Sen. Bernie Sanders (I-Vt.) — or if any anti-Sanders vote will coalesce around him quickly enough to allow him to clinch the nomination.