Democratic presidential candidates from left, Sen. Cory Booker, D-N.J., Rep. Tulsi Gabbard, D-Hawaii, Sen. Amy Klobuchar, D-Minn., South Bend, Ind., Mayor Pete Buttigieg, Sen. Elizabeth Warren, D-Mass., former Vice President Joe Biden, Sen. Bernie Sanders, I-Vt., Sen. Kamala Harris, D-Calif., former technology executive Andrew Yang and investor Tom Steyer participate in a Democratic presidential primary debate, Wednesday, Nov. 20, 2019, in Atlanta. (AP Photo/John Bazemore)

ATLANTA (AP) — Democratic presidential candidates put race at the forefront of their primary scramble Thursday, punctuated by a tense exchange between Pete Buttigieg and Kamala Harris after the white mayor connected his experiences as a gay man to black Americans' long struggle against racism.

Harris, one of three black candidates seeking the nomination, criticized Buttigieg in a post-debate event in Atlanta, calling him "naive" and lambasting him for comparing the struggles of the black and LGBTQ communities. A Democrat who wants a winning coalition "should not be in position of saying one group's pain is equal than or greater to another," said Harris, a California senator.

Buttigieg, the white mayor of South Bend, Indiana, who wed his husband, Chasten, last year, countered that he was not comparing the travails of the LGBTQ community and black America, but instead speaking up for one discriminated class based on his experiences in another.

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Democratic presidential candidate Sen. Kamala Harris, D-Calif., speaks during a Democratic presidential primary debate, Wednesday, Nov. 20, 2019, in Atlanta. (AP Photo/John Bazemore)

The exchange highlights the importance of the black vote in the Democratic nomination process and both candidates' struggles to win them over. It also threatens to expose an uneasy relationship in the party's civil rights coalition, as Democrats increasingly recognize LGBTQ rights as a priority alongside their decadeslong alignment with the civil rights movement for African Americans.

Harris and Buttigieg are among several Democratic candidates trying to dent former Vice President Joe Biden's advantage among black Democrats. Biden met Thursday with a group of prominent black Southern mayors, including Atlanta Mayor Keisha Lance-Bottoms, who has emerged as one of his top campaign surrogates.

Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts held dueling rallies on Atlanta's historically black college campuses, pitching their progressive policy slates to a younger African American audience that is viewed as up for grabs.

Buttigieg has surged to an apparent lead in overwhelmingly white Iowa, which holds the nation's first caucus Feb. 3, but he and his aides acknowledge that he needs to improve on his negligible support in the black community in other states if he hopes to become the nominee. Harris is still trying to crack the top tier in Iowa and beyond, and she used the Atlanta debate Wednesday to make a direct appeal to black women while pitching herself as the ideal nominee to rebuild the multiracial coalition that twice sent Barack Obama to the Oval Office.

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Democratic presidential candidate South Bend, Ind., Mayor Pete Buttigieg speaks about his marriage during a Democratic presidential primary debate, Wednesday, Nov. 20, 2019, in Atlanta. (AP Photo/John Bazemore)

The Buttigieg-Harris flap spun off the mayor saying Wednesday night during a discussion of race that he's often "felt like a stranger" in his own country — a version of a point he makes frequently on the campaign trail when he says he understands what it's like to watch politicians argue over his civil rights.

He clarified his intent Thursday while pushing back on Harris' characterization.

"There's no equating those two experiences — and some people, by the way, live at the intersection of those experiences," he told reporters. "What I do think is important is for each of us to reveal who we are and what motivates us."

Antjuan Seawright, a Democratic consultant in South Carolina, said Buttigieg should expect more scrutiny now that he's a consensus top-tier candidate. But Seawright downplayed any apparent tensions between gay rights and black civil rights.

"I think that our party and our country is made up of the experiences of Kamala Harris and Mayor Pete, so I don't think that Mayor Pete can walk two and a half steps in Kamala's shoes, and I don't know if Sen. Harris could ever walk in the mayor's shoes," he said.

Cory Booker, the other black candidate on the debate stage in Atlanta, avoided weighing in Thursday morning.

Sanders and Warren, meanwhile, also found themselves on the political tightrope of white candidates navigating discussions of race.

Set to deliver a speech on race with a focus on black women, Warren was interrupted at Clark-Atlanta University several times by dozens of black protesters from Powerful Parent Network, a group of school-choice activists. They stood down only after U.S. Rep. Ayanna Pressley of Massachusetts took the microphone from Warren.

"The senator is here to talk about fighters like you," Pressley said, adding that the protesters, in drowning out Warren, were keeping her from telling the story of black women already marginalized.

Warren, buoyed by a gymnasium filled with a boisterous, racially diverse crowd, called for a "full-blown national conversation about reparations" for slavery as she praised black women for helping build the country and advance causes of social and economic justice. And she had blistering remarks for a long run of structural impediments beyond slavery, from Jim Crow segregation to modern-day mass incarceration and red-lining practices that make it harder for minorities to get mortgage loans.

"Black history is American history," Warren said. "And American history teaches us that racism has for generations shaped every crucial aspect of our economic and political system."

She then offered a litany of policy proposals: new spending at historically black schools, repealing the 1994 crime law, legalizing marijuana, overhauling federal housing policy, student loan debt forgiveness.

"I am not afraid," she said to roars. "And you cannot be afraid either."

Sanders, speaking earlier at Morehouse University, leaned on his own biography, like Buttigieg.

"Some of you know, I'm Jewish," Sanders said, as he spoke near the statue of slain civil rights leader Martin Luther King Jr., a Morehouse alumnus. "My father came to this country from Poland. He came fleeing anti-Semitism. A lot of people in my father's family did not make it out of Poland.

"They were murdered by the father of white supremacy, Adolf Hitler," Sanders continued. "So I learned at a very young age what racism and white supremacy and Aryanism and all that crap is about, and our place together is that we will do everything humanly possible to end all forms of discrimination in this country."

Sanders, 78, went on to tell of his 1960s activism, describing himself and his fellow white students as "not quite so brave" as black citizens in the more dangerous Jim Crow South. But, he said, "I was arrested and went to jail fighting housing segregation in Chicago."