The top Democratic White House hopefuls are in a high-stakes race to win the support of black voters, who will play a key role in determining the nominee once the contest moves past the predominantly white states of Iowa and New Hampshire.

That dynamic was on full display at the latest Democratic debate in Atlanta on Wednesday night, as the candidates tailored their policy proposals and emotional appeals to African Americans, who make up two-thirds of the Democratic primary electorate in South Carolina and will be a force on Super Tuesday.

So far, black voters have helped keep former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE afloat, giving him a commanding lead in national polls, as well as in South Carolina, which is fourth in line to vote.

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Sens. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) and Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) have made some inroads in the Palmetto State, but neither boasts the same diverse coalition as Biden, who occupies a special standing among African Americans as the vice president under the nation’s first black president.

And fast-rising South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE may find that he’s hit a ceiling after Iowa and New Hampshire if he can’t figure out how to increase his support from black voters. Polls find Buttigieg at zero percent or in the low single digits among black voters, which will be fatal for his campaign if he is unable to expand his coalition.

The competition will be stiff, as Sens. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.) and Cory Booker Cory Anthony BookerThe movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-N.J.), the only black candidates in the race, hope African American voters find a home in their campaigns, helping propel them into contention down the stretch.

Momentum could play a big role in where black voters ultimately go.

In the 2008 Democratic primary, polls found Hillary Clinton Hillary Diane Rodham ClintonBloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE at about 75 percent support among black voters in South Carolina at this point in the race. After former President Obama pulled off a surprising victory in the Iowa caucuses, black voters flocked to his campaign, leading him to a 30-point victory there.

It is difficult to see that same phenomenon happening for Buttigieg if he doesn’t show some traction among black voters before ballots are cast in Iowa.

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Critics say that Buttigieg had ample time and opportunity to build a coalition of support among black voters as mayor of South Bend, where about a quarter of the city is African American.

But Buttigieg has been beset by racial controversies at home, stemming from his handling of the police department and allegations that his policies have led to white gentrification that has priced poor black people out of their neighborhoods and homes.

“For too long I think candidates have taken for granted constituencies that have been the backbone of the Democratic Party, and overlook those constituencies, and show up when it’s close to election time, show up at a black church and want to get a vote,” Harris said in one exchange with Buttigieg at the debate.

Buttigieg said that he has “lived and breathed the successes and struggles of a community where far too many people live with the consequences of racial inequity.”

He sought to draw a line between racial injustice and his own experience as a gay man in America.

“I do have the experience of sometimes feeling like a stranger in my own country, turning on the news and seeing my own rights come up for debate, and seeing my rights expanded by a coalition of people like me and people not at all like me, working side by side, shoulder to shoulder, making it possible for me to be standing here,” Buttigieg said.

Warren has also struggled to attract support from black voters, as polls find her base of support is dominated by well-educated white liberals.

The Massachusetts Democrat, who burst to the top of the field but has been sliding in recent weeks, is pinning her hopes of success among black voters on her policy proposals, which have been a hit in Iowa and New Hampshire.

At Wednesday’s debate, Warren touted her plan to build 3.2 million new government housing units for poor people, arguing that “the federal government has subsidized the purchase of housing for decades for white people and has said for black people you're cut out of the deal.”

And Warren said black people are more likely to borrow money for college and have a harder time paying back the loans once they graduate. She pointed to her student loan forgiveness plan as an example of how she would focus on helping black Americans by "closing the black-white wealth gap.”

Sanders, meanwhile, routinely polls in second place among black voters, although he is far behind Biden.

The Vermont senator has attracted a diverse group of black surrogates, including rapper Killer Mike and former Ohio state Sen. Nina Turner.

Sanders is almost always on message about social stratification, no matter what group he’s addressing. At the debate, Sanders pointed to voter suppression and big money in politics as issues that have contributed to the marginalization of black people in the U.S.

He also closed the debate with a story about his time with a civil rights group at the University of Chicago, where he was arrested as part of “the fight against all forms of discrimination.”

Harris and Booker see an opening here as well.

On Wednesday night, Harris pushed the idea that as a woman of color, she is best equipped to “rebuild the Obama coalition.”

“I believe that we have to have leadership in this country who has worked with and have the experience of working with all folks,” Harris said. “And we've got to re-create the Obama coalition to win.”

Booker, meanwhile, returned to racial inequality in nearly every question he answered.

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The New Jersey Democrat talked about how both of his parents attended historically black universities, said black voters are “pissed off and worried” that Democrats will nominate someone who “doesn’t have authentic connection” to them, attacked Biden for opposing marijuana legalization and attacked Warren for obsessively focusing on taxing the wealthy rather than on building wealth for racial minorities.

“I have a lifetime of experience with black voters,” Booker said. “I’ve been one since I was 18.”

For Biden, the stakes are clear — he must maintain his level of support from black voters, who appear to be buttressing him against a deep slide.

At Wednesday’s debate, the former vice president flubbed a line aimed at showcasing his support from black voters by saying he had the endorsement of the only black woman ever elected to the Senate, seemingly forgetting Harris.

But Biden’s broader point was true — a strong plurality of African Americans are with him at the moment.

The question is whether their loyalty will persist if he has poor showings in Iowa and New Hampshire.

“I'm part of that Obama coalition,” Biden said. “I come out of a black community, in terms of my support. If you notice, I have more people supporting me in the black community that have announced for me because they know me, they know who I am.”