ATLANTA — One day after a televised debate featuring significant exchanges about race, Democratic presidential candidates fanned out across this capital of black political power to pitch their message to black voters and send a clear signal: Former Vice President Joseph R. Biden Jr. should not take support from African-Americans for granted.

Mr. Biden’s strength with black voters has been a key force in helping him maintain a polling edge in the race, even as the candidacies of Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont ascended among progressives. But on Thursday, both challengers — as well as Senators Kamala Harris and Cory Booker, two black candidates in the race, and other contenders — made explicit appeals about how they would address concerns and priorities of black voters.

Ms. Warren, who is Mr. Biden’s leading rival in many state and national polls, took direct aim at his reliance on black support by delivering one of her biggest speeches of the campaign, describing how governments and powerful corporations use racism and racial injustice as a wedge to divide working-class people. And she argued that it was time for the nation’s policies to include specific correctives to address discrimination.

“Don’t talk about race-neutral laws,” she said at a rally on Thursday evening at Clark Atlanta University, a historically black institution. “The federal government helped create the racial divide in this country through decades of active, state-sponsored discrimination, and that means the federal government has a responsibility to fix it.”

“The rich and the powerful want us to be afraid of each other,” Ms. Warren told the crowd. “And why? Because they are afraid of us. Afraid of our numbers. Afraid of seeing us stand together.”

Ms. Warren also spoke directly to white voters, and pushed back on the notion that racial equity comes at the cost of white Americans.

“I just want to speak directly to the question on some white people’s minds when we talk about the need to address what our government has done in black communities: the uncomfortable question of, ‘What will this mean for me?’” Ms. Warren said. “The truth is, when we come together, we can all move forward.”

Ms. Warren’s speech was a thematic continuation of her rally in New York City in September, when she used the Triangle shirtwaist factory fire of 1911 to tell a story of government regulation and the political power of women’s voices. In her speech on Thursday Ms. Warren leaned on history again, citing the black women-led strike of Atlanta washerwomen in 1881.

Ms. Warren was introduced by Representative Ayanna S. Pressley of Massachusetts, the black lawmaker who has become one of Ms. Warren’s top surrogates after her recent endorsement. Ms. Pressley helped Ms. Warren calm a group of pro-charter school protesters who disrupted her speech.

Earlier that day, several other candidates also targeted black voters, speaking at a breakfast held by the Rev. Al Sharpton’s National Action Network. Ms. Harris attended a “black women power breakfast” with several of Atlanta’s leading black women professionals. And Mr. Sanders also held a rally on the campus of a historically black college.

At Morehouse College, standing near a statue of the Rev. Dr. Martin Luther King Jr., Mr. Sanders invoked his own background in a pitch to black voters. As a Jewish man whose family escaped Nazi Germany, he learned about the cruelties of racism through his family’s stories of fleeing discrimination, he said.

“A lot of people in my father’s family did not make it out of Poland, and they were murdered by the father of white supremacy, Adolf Hitler,” he said.

Black voters are an important constituency in the Democratic Party, and the candidate who has won a majority of the black vote has almost always gone on to be the party’s nominee. But in a race with multiple black candidates and with white candidates promising policies specifically addressing racial inequities, the diversity of the black electorate — with respect to age, gender, education levels and ideology — has been on display.

Still, it has been difficult for candidates to wrest black support away from Mr. Biden. He has been buttressed by sky-high name recognition, association with former President Barack Obama and his promise that he is best suited to win the white working-class voters who helped deliver the last election to President Trump.

On Thursday, Mr. Biden met with a group of black mayors, including Keisha Lance Bottoms of Atlanta, who has endorsed him, before leaving for a town hall event in South Carolina, an early primary state where he leads in the polls.

Speaking to reporters in Atlanta, Mr. Biden cited his long relationship with the African-American community in Delaware when asked about his support among black voters. “I’ve always been comfortable in the community, and I think that the community’s always been comfortable with me,” Mr. Biden said.

In Wednesday night’s debate, Mr. Booker criticized Mr. Biden for his opposition to legalizing marijuana, noting that black marijuana users are more frequently penalized than white ones.

“Black voters are pissed off and they’re worried,” Mr. Booker said, adding that while he had “a lot of respect” for Mr. Biden, “this week I hear him literally say that ‘I don’t think we should legalize marijuana.’”

Looking directly at Mr. Biden, Mr. Booker said, “I thought you might have been high when you said it.”

At a ministers’ breakfast meeting sponsored by the National Action Network, Mr. Booker continued his pitch a day later as the best candidate to address racial inequities in the economy and criminal justice.

“The black-white wealth gap is growing. The leading cause of death for African-American boys and men is murder,” Mr. Booker said. “We are at a point now that there’s more African-Americans under criminal supervision than all the slaves in 1850.”

A number of other candidates also toured Atlanta, making a concerted pitch to black voters. Senator Amy Klobuchar of Minnesota, Mayor Pete Buttigieg of South Bend, Ind., the entrepreneur Andrew Yang and the billionaire former hedge fund manager Tom Steyer attended Mr. Sharpton’s breakfast, too.

Mr. Buttigieg sought to establish common ground with the black audience, pointing out that, as a gay man, he had benefited from black activism during the civil rights movement.

But he has struggled to build support among this constituency. A recent South Carolina poll showed he is the choice of fewer than 1 percent of black likely Democratic voters there.

Ms. Harris held a morning breakfast event for black women in Atlanta. Though her candidacy has fallen from its once front-runner status, Ms. Harris made clear that she remains the only black woman in the race, and pitched herself as someone who can uniquely understand black communities.

“There are people on that debate stage who wrote the crime bill, who voted for the crime bill and who have not had the language to know what this is about until just the last couple years. Are you kidding me?” Ms. Harris said. “Where were these folks when I was creating a national model around what we need to do to end mass incarceration and the war on drugs?”

At the debate, Mr. Biden touted his support among black voters, saying, “I come out of the black community in terms of my support.” But then he mistakenly said he had the endorsement of the “only African-American woman that had ever been elected to the United States Senate.”

He was apparently referring to former Senator Carol Moseley Braun of Illinois — the first black woman to become a senator.

He failed to mention Ms. Harris, the second black woman elected to the Senate, who was standing on the same stage.

Stephanie Saul contributed reporting from New York.