Attempting to rebound from losses in the Iowa caucuses and the New Hampshire primary, former vice president Joe Biden has said that his status in the Democratic presidential race can’t be assessed until after we’ve “heard from the most committed constituency of the Democratic Party — the African American community.” He’ll get his chance in this week’s South Carolina primary, where black voters are around 60 percent of the Democratic electorate.

Recently, Biden argued, “I’m the only one who has the record and has the background and has the support” of the black electorate. Indeed, for much of this campaign season, polls showed Biden was favored among black voters: A January Washington Post-Ipsos poll found 48 percent of black Democrats supported Biden, but in the latest Post-ABC News poll, Biden’s African American support fell to 31 percent. Biden’s claim of the importance of the black electorate to Democratic wins and his — or any Democrat’s — challenge in securing the black vote reveals a quandary about black voters: Does their overwhelming support for Democrats in general election contests tell us anything about how they’ll decide in primaries?

It does.

As we show in our new book, “Steadfast Democrats: How Social Forces Shape Black Political Behavior,” the generally unified preference among black Americans for Democratic candidates (in 2016, according to exit polls, the Democratic nominee, Hillary Clinton, won 88 percent of the black vote, compared with 8 percent for Republican Donald Trump) reflects not unified political preferences, but a social process by which black Americans hold one another accountable for voting in favor of the party that is understood to best represent the group as whole. In short: In general elections, norms of Democratic Party support constrain black electoral preference.

This isn’t to suggest the absence of some fairly wide policy agreements among African Americans, but rather that without this social process, the degree of partisan unity at the polls would not hold.

The lesson to take from what we know about why black voting is steadfastly Democratic in general elections, and to apply to the primaries, is that candidates seeking to consolidate bloc-like support from black voters have a twofold job. First, without party identification as a shortcut for political decision-making, the candidates have to prove to black voters that they have unique claim to the likelihood that they will represent the interests of the black community. Second, they need to show that they can deliver on the black community’s understood interest in beating the Republican, particularly President Trump, in the general election. These two criteria can consolidate the impression that a particular candidate is clearly best for the group. For most of the primary season, it seemed as though the benefit of that impression accrued to Biden. But if no Democrat emerges as the clearly dominant choice for the group interest, then African American primary voters have reason to make choices using other criteria. And among black voters, there are plenty of sources of political difference.

For much of the past year, Biden seemed poised to win on both these dimensions. His time serving with, and personal connection to, President Barack Obama, coupled with Biden’s initially strong polling support among Democrats overall, helped position him as the candidate seen to be both potentially responsive to black group interest and most capable of winning in November. The results in Iowa and New Hampshire, however, have made it harder for Biden to maintain that he’s the most electable. Coupled with Biden’s subpar record on criminal justice issues and his mishandling of Clarence Thomas’s Supreme Court confirmation hearings, the case for Biden as a champion of black interests has clearly been damaged.

While it may be too early to say whether black support for Biden has collapsed, there is reason for his campaign to worry going into South Carolina. Clinton was initially seen as the safe bet for black voters in 2008 — in the run-up to that year’s primaries, polls showed she led Obama by wide margins among African Americans. But an early loss in Iowa that year began the gradual erosion of her support among black voters and gave Obama, then cast as a fresh, barrier-breaking contender, the momentum. Unlike 2008, though, there’s no Obama in 2020 for black voters to unify around. The most likely outcome, then, is the black vote splits and leaves black voters attempting to identify the candidate who will focus on policy issues of specific concern to black Americans, and less coalesced around a candidate mainly seen as having the best chance of beating Trump in November.

Among those black Americans who value more a candidate who is committed to representing black group interest — specifically, reducing inequality in education, wealth and health outcomes — we expect a shift in their support toward candidates like current front-runner Sen. Bernie Sanders (I-Vt.) or Sen. Elizabeth Warren (D-Mass.). This set of issues squares with both Sanders’s and Warren’s platform promises of (differing versions of) Medicare-for-all, federally subsidized college tuition and combating economic inequality.

While many black Americans find political common ground in Warren and Sanders, many also worry about whether either of them can muster enough white support to beat Trump — the electability question looms. In a Feb. 10 Quinnipiac poll, 85 percent of black voters said they would vote for either Warren or Sanders in a head-to-head matchup with Trump. But by contrast, when asked in the same poll which candidate they thought had the best chance of winning against Trump, only 14 percent placed their confidence in Sanders and a mere 2 percent chose Warren. The two candidates that African Americans saw as most likely to beat Trump were Biden (40 percent) and former New York mayor Mike Bloomberg (25 percent), who initially ran for office as a Republican.

Despite his poor performance in Tuesday’s Democratic debate, Bloomberg’s recent rise is perhaps most revealing about the trade-offs black voters face in the Democratic primary. As a mayor who, for years, embraced and perpetuated a stop-and-frisk policy that targeted African Americans and Latinos, Bloomberg is not well liked among black Americans. The January Post-Ipsos poll found Bloomberg had only a 29 percent net favorability rating among African Americans (with the caveat that many of those polled had either never heard of him or had no opinion) — compared with 69 percent for Biden, 63 percent for Sanders and 51 percent for Warren. In the same poll, among registered black voters, nearly 14 percent reported they wouldn’t vote in the general election if Bloomberg were the Democratic nominee — compared with 6 percent for Biden, 8 percent for Sanders and 10 percent for Warren. Lastly, when asked who would be the best candidate at addressing issues that are important to the black community, only 3 percent of black Democrats identified Bloomberg as the best, compared with 32 percent who selected Biden and 19 percent who chose Sanders.

Black support for Bloomberg is far from negligible, but it is driven by the same electability considerations that once heavily favored Biden. Many of Bloomberg’s priorities remain at odds with more policy-grounded group interests of black Americans.

So, Biden’s last glimpse of viability may lie in South Carolina, and in his campaign’s capacity to convince black voters there that he really can satisfy — at least more than any current alternative — their joint demands of electability and group interest. Although Bloomberg appears to have convinced nearly a quarter of the African American electorate that his money and its power will translate into broad appeal among white voters in the general election, in the South Carolina primary, Bloomberg is not on the ballot.