Democrats Have the Most Racially Diverse Field Ever. The Top Tier Is All White.

If Mr. 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 Mr. Biden, like Mr. Buttigieg and Senator Amy Klobuchar of Minnesota, have posted dismal numbers with nonwhite voters.

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

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

Ms. Warren, of course, would be barrier-breaking in her own right as the first woman to be president, as would Mr. 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, Mr. Sanders, Ms. Warren, Mr. Biden and Mr. Buttigieg have $90 million in cash on hand. Ms. Harris, Mr. Booker, Mr. Castro, Andrew Yang, the Asian-American entrepreneur, and Tulsi Gabbard, the American-Samoan Congresswoman, have about $24 million combined.

Mr. Booker and Mr. 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 Representative Alexandria Ocasio-Cortez of New York, who alluded to the importance of racial representation.