ATLANTA — Cory Booker was roaring through metaphors Thursday, quoting Scripture and Langston Hughes to a chorus of “Amen!” and “Preach!” in a room full of African American ministers, when a door opened a few feet away.

A staffer ushered in South Bend, Ind., Mayor Pete Buttigieg, who hunched over to sneak past Booker, trying not to interrupt or offend. He took a seat next to the Rev. Al Sharpton, then stood and clapped politely as the audience rose to its feet in raucous applause for Booker’s stemwinder.

Toward the back of the room, an attendee observed the entrance of Buttigieg, who was set to follow Booker onstage. “Pete’s like, ‘What the hell am I going to do now?!’ ” he mused to a friend, and the two dissolved in laughter.

Buttigieg and Booker were just two of the Democratic candidates fanning out across Atlanta and the South on Thursday, following Wednesday’s contentious debate in that city, in an increasingly urgent effort to court black voters. The multiple events highlighted a puzzle central to the Democratic primary: Can anyone chip away at black voters’ support for former vice president Joe Biden — and if not, what does it mean for the Democrats’ ­chances?

“They’re pissed off, because the only time our issues seem to be really paid attention to by politicians is when people are looking for their vote,” Booker said Wednesday in describing the mood of black voters.

Sen. Amy Klobuchar (D-Minn.) and businessmen Andrew Yang and Tom Steyer appeared at Thursday’s gathering of African American ministers, sponsored by Sharpton’s National Action Network, alongside Booker and Buttigieg. A few minutes away, Sen. Kamala D. Harris (D-Calif.) hosted a Black Women Power Breakfast.

Sen. Bernie Sanders (I-Vt.), taking the stage at a rally at Morehouse College, unveiled a plan to increase funding to historically black colleges and universities. Sen. Elizabeth Warren (D-Mass.) delivered a speech centered on the contributions of black women throughout history.

And several of the candidates headed to Ebenezer Baptist Church, where the Rev. Martin Luther King Jr. once preached, to take part in a phone bank organized by former Georgia gubernatorial candidate Stacey Abrams, one of the party’s African American stars.

Thursday also saw some Democrats turning on each other on racial issues, with increased pressure to make headway before the Feb. 3 Iowa caucuses. Harris said it had been “misdirected” for Buttigieg, at the debate, to refer to his experience as a gay man during a discussion of racial issues; Buttigieg responded that he hadn’t been equating one experience to the other.

Nina Turner, a co-chair of the Sanders campaign, took aim at Biden, playing down his service with President Barack Obama, which Biden often touts, especially to black audiences. Sanders “doesn’t believe that proximity to a black president gives one person more right to get the black vote than anybody else,” Turner said.

Buttigieg, as a 37-year-old white man in charge of a small Midwestern town, arguably faces more pressure than most to convince black voters that they can trust him. He has been gaining momentum in the Democratic race, but without African American support, his path to the nomination is challenging, if not impossible.

In the most diverse field in presidential history, Buttigieg has less experience handling racial issues than many of his competitors, and he has made several missteps during the campaign. While his support has grown in Iowa and New Hampshire — where more than 90 percent of Democrats are white — he is struggling in South Carolina, with its sizable black population.

A recent Quinnipiac University poll found Buttigieg receiving less than 1 percent support among likely black voters in the state.

At Sharpton’s event Thursday, Buttigieg said that as a gay man, he recognizes that his rights were expanded by the advocacy of others. That, he said, “is why I understand my obligation to do everything in my power, as a candidate and as a president, to bring about a sense of belonging and to put an end to systemic racism in this country before it puts an end to the entire American project.”

Sharpton praised Buttigieg for reaching out to him on racial issues.

“He was open and candid. He called me — we didn’t call him,” Sharpton said. “I think that he has brought a very serious and thought-out vision into this campaign. Wherever it ends up, I think we will be hearing from Mayor Pete — or who knows, another title — for a long time.”

Warren, in her speech at Clark Atlanta University, one of the oldest HBCUs in the country, was joined by Rep. Ayanna Pressley (D-Mass.), an African American lawmaker who has endorsed her. Warren was careful not to compare her experience with that of African Americans.

“As a white woman, I will never fully understand the discrimination, pain and harm that black Americans have experienced just because of the color of their skin,” Warren said. “I’m not here to tell you about a painful history that black Americans experienced and know all too well. I am here today for a different reason. I’m here to make a commitment: When I am president of the United States, the lessons of black history will not be lost.”

The speech was disrupted several times by a group of more than 100 black activists pushing for school choice. “We value our children’s education,” said Sarah Carpenter of Memphis, a spokeswoman for the group. “If you don’t listen to us, we are going to raise our voice.”

Biden met Thursday with Democratic mayors of Southern cities, several of whom had written the candidates in September saying they needed to provide detailed plans for addressing these cities’ challenges if they hoped to get an endorsement.

Richmond Mayor Levar Stoney, one of those who met with Biden, said the session went well but was just a start.

“I thought it was a good discussion, but I think a lot of us still want to have more discussions,” Stoney said. “This is hopefully the first of many talks we will be having with the vice president.”

Stoney eventually plans to make an endorsement in the presidential race, and he said he would be guided heavily by how his constituents feel. For the moment, “I don’t see that sort of coalition coming together for Mayor Buttigieg,” Stoney said. “I think a lot of my constituents just don’t know him.”

Biden, he said in contrast, “is a household name.”

Buttigieg is hardly the only candidate struggling to garner black support. But his rivals have begun seizing on that vulnerability to dispute Buttigieg’s suggestions that he can bridge the nation’s divides, with some questioning how electable he is without African American support.

The carefully chosen words Buttigieg uses to address those concerns have not overcome a range of problems and missteps during the campaign. In June, a white police officer in South Bend shot a black man, prompting protests against Buttigieg by black activists and forcing the mayor to leave the campaign trail for some time.

More recently, some black leaders in South Carolina expressed frustration when Buttigieg’s campaign listed them as endorsing his “Douglass plan” for racial justice, saying the campaign had overstated their level of support. And his campaign recently had to answer for using a stock photo of a Kenyan woman as part of its outreach to black voters.

Harris used that incident to argue during the debate that the Democratic nominee must be comfortable in diverse communities and suggested that some of her rivals were not.

“The question has to be, where you been? And what are you going to do? And do you understand who the people are?” she said.

In a sign of their growing importance, racial issues underlined some of the debate’s sharpest exchanges. Booker, apparently referring to leaked reports of a Buttigieg campaign focus group on black voters, declared, “Nobody on this stage should need a focus group to hear from African American voters.”

He added that he thought Biden must have been “high” to oppose marijuana legalization, given the effect of the drug war on minorities.

Harris and Booker are both prominent African American political figures, but they also have struggled to attract significant support from black voters. In an apparent effort to change that, both Harris and Booker ramped up their rhetoric on racial issues Wednesday night.

Biden, for his part, boasted that he has more support from black leaders than any other candidate — “because they know me, they know who I am.” He called himself “part of that Obama coalition.”

But Biden also mistakenly said he had been endorsed by the only African American woman ever elected to the Senate, a reference to former senator Carol Moseley Braun (D-Ill.). The second African American woman elected to the Senate — Harris — was standing a few feet away.

The Warren and Sanders campaigns have both acknowledged the need for further outreach to black communities, and they are relying on high-profile surrogates to help build credibility. Activist Phillip Agnew joined Turner, the Sanders co-chair, for a tour of HBCUs in the days leading up to the debate, and both appeared with Sanders at Morehouse on Thursday afternoon.

Turner often speaks of Sanders’s longtime involvement in the civil rights movement, and some of his supporters wear T-shirts featuring Sanders getting arrested at a protest while in college.

Birmingham, Ala., Mayor Randall Woodfin, one of those who met with Biden on Thursday, is not backing a particular candidate, but he said that Buttigieg has reached out to him and that the two might meet in Birmingham later this year.

Asked why Buttigieg has not connected with black voters, Woodfin said, “It’s not necessarily why black voters are not connecting with another candidate.” Rather, he said, “there is a candidate in the race that is appealing to black voters because there is a sense of already knowing — a relationship,” meaning Biden.

Fayetteville, N.C., Mayor Mitch Colvin, however, said there appears to be some skepticism in African American communities about Buttigieg.

“We may have to get to know him a little better,” he said.

Annie Linskey contributed to this report.