When the Democratic primary contest began last winter, it featured the most racially diverse field in history, with two black senators, a Latino former Cabinet secretary, an Asian-American businessman and the first American Samoan elected to Congress. But 10 months later, the Democratic field has a top tier of four white candidates, three of them men.

Candidates of color are languishing in the low single digits in polls, well behind the four leaders — former Vice President Joe Biden, Sens. Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont, and Mayor Pete Buttigieg of South Bend, Indiana. The divide could become even more pronounced in the coming months: Because of new, more rigorous thresholds for the Democratic debate in December, it is possible that only one nonwhite candidate, Sen. Kamala Harris of California, will qualify.

With the Iowa caucuses three months away, it’s a noticeable sorting of the field for an increasingly multiracial party, whose most recent White House victories were powered by a strong minority turnout for a black nominee. It has frustrated the Democrats seeking a more diverse party leadership — not to mention the affected candidates.

“I’ve had lots of crazy things said to me, like, ‘Is America ready for another black president?’” Sen. Cory Booker of New Jersey said in an interview. “And I’m confident it’s never been asked of a white candidate, ‘Is America ready for another white president?’”

The emergence of an all-white top tier reflects a combination of factors at the intersection of race, money and politics.

Financial support from mostly white, educated elites has helped propel the candidacies of Warren and Buttigieg, while two nonwhite candidates — Booker and Julián Castro, the former housing secretary — have had to explicitly petition supporters for money to stay in the race.

Assumptions about which candidates can or can’t beat President Donald Trump have also hurt minority candidates, with some Democrats fearing that the white working class voters who helped propel Trump to the White House would not support a nonwhite nominee. Donors for Booker and Harris have argued that such implicit bias causes voters and pundits to treat Buttigieg as the natural heir to Biden’s moderate coalition, though their candidates perform better among older black voters, the Democrats’ most loyal moderate voting block.

Other Democrats, however, say the blame rests with the candidates themselves. None of the nonwhite challengers have been able to forge a strong coalition or peel away black voters from Biden. Some voters and elected officials, white and nonwhite alike, say privately what the polling suggests: They have not been swept off their feet by any of the candidates of color.

Theodore Johnson, who studies African-American politics at the Brennan Center for Justice, said the nonwhite contenders, fairly or not, are suffering in comparison to the country’s first black president.

“Their road is easier because of Obama, but their ability to secure the nomination is harder because they’re not Obama,” Johnson said.

Miscalculations along the way have not helped. Harris has been criticized for waffling on policy, Booker for timidness and Castro for a failed debate attack on Biden in September, which cost him the endorsement of one of his few congressional allies.

Castro, in an interview, zeroed in on “electability” as a problem, saying that concept has created an unspoken skepticism of nonwhite candidates among Democratic voters. People with this viewpoint, he said, can sometimes see nonwhite candidates as vice-presidential options, but not best equipped to lead the party.

“In every election there’s a current, and the current this year seems to be running toward candidates that people believe can take Donald Trump on with a certain profile of voter — the white working class in the Midwest,” said Castro, whose polling support is running at about 1%.

And, he added, “assumptions are being made on who the best type of candidates are to do that.”

Booker said he thinks the tide will turn as more people seek a strong candidate to replace Biden as the moderate alternative to Warren and Sanders. The trouble: getting enough financial support over the next two months to remain viable.

“I have to say this last few weeks, a lot of — a lot more people seem to be coming around,” Booker said, “and I think some of this might be because they’re seeing some weakness to Biden.”

Aimee Allison, founder of She the People, the network of women of color looking to mobilize for the 2020 general election, said it was too early to rule out unforeseen shifts in the race’s current pecking order. But she added that it would take more than an argument for racial representation to win over voters of color and rise in the polls.

“We’ve never had choices like this before, and that makes essentialism less important,” she said. “There’s diversity of opinion. Women of color are sophisticated voters and organizers. We understand that our power and influence can be felt through a candidate of any race and gender with our agenda.”

Any assessment of the performance of nonwhite candidates is complicated by Biden’s enduring appeal with black voters. The former vice president remains popular from his time in the White House serving with President Barack Obama, and he benefits from the perception among many Democrats that he has the best chance to win back white voters who flipped to Trump.

That popularity with African-Americans has helped keep Biden at or near the lead in the race for months, while preventing candidates like Booker and Harris from making inroads in states like South Carolina. One recent poll gave Biden a 17-point lead over his closest rivals in the state, propelled by the support of about 40% of black voters.

Even left wing activists who prefer other candidates acknowledge Biden’s advantage will be difficult to overcome.

“Like many black homes in America, my parents’ home has an Obama shrine,” said Tamika Gadsden, a South Carolina-based activist who likes Warren and Castro but whose parents side solidly with Biden.

If Biden falters in predominantly white states that vote earlier, there’s no guarantee that black voters will desert him — or that their support would automatically go to the race’s black candidates. And the white candidates positioning themselves as moderate alternatives to Biden, like Buttigieg and Sen. Amy Klobuchar of Minnesota, have posted dismal numbers with nonwhite voters.

Likewise, the candidates vying for the progressive lane, Warren and Sanders, still face heavy skepticism among the older black voters.

“It’s still early,” said Rep. Karen Bass of California, the head of the Congressional Black Caucus, “I don’t take the top four as the fait accompli.”

Warren, of course, would be barrier-breaking in her own right as the first woman to be president, as would Buttigieg, an openly gay man. Both have risen to the top tier of early-state and national polls, and both are flush with cash from a largely white donor network that has assured them of long-term viability.

Together, Sanders, Warren, Biden and Buttigieg have $90 million in cash on hand. Harris, Booker, Castro, Andrew Yang, the Asian-American entrepreneur, and Tulsi Gabbard, the American-Samoan congresswoman, have about $24 million combined.

Booker and Castro have, in recent weeks, had to make desperate hat-in-hand pleas for money just to stay in the race, and both received online boosts from prominent black and Latino politicians including Stacey Abrams of Georgia and Rep. Alexandria Ocasio-Cortez of New York, who alluded to the importance of racial representation.

The race could quickly change before voting begins in February. Harris has more money in the bank, and more endorsements from the Congressional Black Caucus, than Biden. Castro has not qualified for the November debate, but Booker and Harris have — and will have more opportunities to catch fire before the Iowa caucuses, which will reshape all expectations in a single night.

Conversely, while none of the leading white candidates have proved they can forge a multiracial coalition, they still have time to make inroads. Warren has gained good will from black and Latino progressives for infusing her policy proposals with planks about racial equity. Sanders has a vast and diverse donor base, and recently won endorsements from three of the country’s most prominent minority lawmakers, Ocasio-Cortez and Reps. Ilhan Omar of Minnesota and Rashida Tlaib of Michigan.

Harris, Castro, and Booker are inhibited in part because they came up through the Democratic establishment, and have faced criticism for legislative records that are viewed as out of step with the ascendant progressive wing.

Castro, in response, has tried to remake himself as a progressive champion, and even disavowed some of the deportation actions of Obama’s administration, in which he served. Harris and Booker have tried to tow a more careful line, in hopes they can win more moderate black voters should Biden falter.

Booker has been attacked for his closeness to big donors and mixed police reform record as mayor of Newark, New Jersey. Harris’ lack of clarity on policy has drawn fire, both from left-wing activists upset with her record as a prosecutor and centrists annoyed that she backed left-wing ideas such as the Green New Deal.

Because of this, some black and Latino Democrats push back on the idea that it’s racism or assumptions about electability that have hindered Booker, Harris and Castro. Privately they claim that some nonwhite Democrats who decided not to run, such as Abrams of Georgia or Andrew Gillum of Florida, would have been stronger candidates.

“It boils down to the candidates themselves,” said Rep. Filemon Vela of Texas. “Those structural barriers existed when President Obama ran.”

Vela, for his part, is backing Biden, convinced that he’s best suited to defeat Trump.

But he thinks a woman of color should be on the ticket and he has one in mind: Sen. Catherine Cortez Masto of Nevada.