(Bloomberg) -- Joe Biden tried to defend his record on the most emotional issue in American life -- race relations -- with a recitation of state’s rights and senatorial procedure and got caught by a candidate who could speak in personal terms of how the nation’s long struggle with prejudice affected her.In the most dramatic moment in Thursday’s Democratic presidential debate in Miami, Senator Kamala Harris, 54, questioned Biden, 76, over his role opposing federal enforcement of the school busing policies she credited with affording her a quality education. The exchange highlighted the racial and generational divides between the Democrats seeking to win their party’s nomination and face President Donald Trump in November 2020.Biden, the current front-runner, stood stone-faced as Harris said she was hurt by his earlier comments defending his collegiality and cooperation with Southern senators who were known segregationists. She added that as a child growing up in California she was part of the second class of kids bused to a different school to integrate her city’s public education system.Biden can rightfully point to a record advancing civil rights, but it is blotted by anti-busing language he included in 1975 legislation to block a federal agency from using taxpayer money to compel communities to bus students to desegregate schools. Biden tried to defend himself on the debate stage, calling Harris’s comments a “mischaracterization of my position across the board” -- drawing a distinction between busing and federal enforcement of the practice.The frosty exchange came at a time when Harris is trailing Biden, Senator Bernie Sanders of Vermont, and Senator Elizabeth Warren of Massachusetts in polls. Her strategy includes appealing to black voters who are key to winning states in the South, including the early primary state of South Carolina where 60% of Democratic voters are African-American.The dialogue between Harris and Biden also revealed how well they prepared -- or didn’t -- for the debate. After Harris told her personal story, her campaign tweeted a decades-old picture of the candidate in pigtails.The race question was an obvious one for Biden to anticipate, following his earlier comments about working with segregationist lawmakers. Yet Biden’s defense of his 36-year Senate career fighting for civil rights and extending the Voting Rights Act sputtered to a stop when he acknowledged the moderators and said: “My time is up. I’m sorry.”The confrontation was kicked off by a question for South Bend, Indiana, Mayor Pete Buttigieg about the recent police shooting of a 54-year-old black resident in his city, which exposed racial tensions there.Buttigieg was pressed about why he hasn’t improved representation on the South Bend police force that is 6% black, in a city that is 26% black. He responded honestly and bluntly: “Because I didn’t get it done.”The 37-year-old mayor, who has stepped up his own outreach to African-American voters, went on to say his community is in anguish, adding that “it’s a mess, and we’re hurting.”Harris stepped in and insisted on speaking of the topic of race and community policing as the only person of color on the debate stage. Moderator Rachel Maddow offered her 30 seconds to make a point that wound up extending well beyond that boundary and may have won her the debate.”I otherwise have a great deal of respect for Joe Biden,” Harris told MSNBC after the debate. “I do not believe he’s a racist, but his perspective on those senators was something that was hurtful and it had consequences.”To contact the reporters on this story: Laura Litvan in Washington at llitvan@bloomberg.net;Gabrielle Coppola in New York at gcoppola@bloomberg.netTo contact the editors responsible for this story: Joe Sobczyk at jsobczyk@bloomberg.net, Anna Edgerton, John HarneyFor more articles like this, please visit us at bloomberg.com©2019 Bloomberg L.P.