Driving the news: Last week, a group of more than 100 black female activists endorsed Warren for president, calling her a "leader" whose policies, track record, and understanding of structural inequality speak directly to black voters.

Biden's proximity to former President Barack Obama contributes to his high support among older black Democrats — but he hasn't convinced young black voters.

What they're saying: "She's the only one who consistently leaves the room with more support than whatever she came in with," Cliff Albright, co-founder of the Black Voters Matter Fund, told Axios. "The exact opposite is the case for Joe Biden."

Albright said that whether at debate watch parties or presidential forums specifically for black voters, "I haven't met anybody — activists, regular voters, even some of his supporters — who after hearing him come out doubling down on their support for him."

Adrianne Shropshire, executive director of BlackPAC, told Axios that Biden may have some vulnerabilities with black voters because of his record on things like busing, working in past decades with segregationists in the Senate, and the way he treated Anita Hill nearly three decades ago during her testimony.

Still, Shropshire said: "Biden was in the fight with Barack Obama, and black voters see him as being a defender of Barack Obama and his legacy."

Antjuan Seawright, a South Carolina-based Democratic strategist, told Axios that Biden's support among black voters is solid and deep, based on relationships, accountability, familiarity and trust. "Those are the golden eggs that Biden has found throughout his career that make people believe in him and trust in him.“

Axios tracked nine Quinnipiac surveys between March and the end of October for black Democrats' support of 2020 primary contenders, and found:

Warren has steadily been gaining support among black Democrats along with her overall rise in the nominating contest. She had less than 0.5% support from black Democrats in March; by the end of October that had risen to 20%.

Biden as of the end of October was at 43%, about where he started in March.

These numbers can only give us a general idea of support, since the sample sizes were small — ranging from 62 to 105 people in each survey — and the margin of error ranged from ±11.4% to ±14.8%.

That range is high because the samples were culled from national surveys of all voters, then narrowed to Democrats, then narrowed to black Democrats.

Doug Schwartz, director of the Quinnipiac University Polls, said the survey information still has value because it shows trends. Biden’s numbers are relatively consistent throughout, and he said the results are consistent with other polls of black voters.

The intrigue: The black vote is a potent factor for the rest of the Democratic field.

Julián Castro has been publicly going after Pete Buttigieg, arguing that Buttigieg doesn't have a great track record with black voters in South Bend, Indiana.

Buttigieg's top-tier national status has frustrated some in the black community given that he's earned an average of less than 1% support among black Democrats across the 9 Quinnipiac polls. "If you only had 1% of the white vote nobody would call you a frontrunner," Albright said.

It's too soon to say how the entry into the nominating contest of former Massachusetts Gov. Deval Patrick, who is black, will be received by black voters.

Reality check: Strong backing from black voters in the primary doesn't guarantee a win in the general election. Just ask Hillary Clinton.

Editor's note: This story has been updated to include a quote from Democratic strategist Antjuan Seawright.