Former Vice President Joe Biden flatly denied he had opposed school busing in a dramatic exchange with Sen. Kamala Harris during the first round of Democratic primary debates on Thursday.

Harris confronted Biden over his comments about working with pro-segregation senators and his opposition in the 1970s to the busing of students of color to predominantly white schools.

Biden defended his record and denied Harris' charges, saying, " I did not oppose busing in America. What I opposed is busing ordered by the Department of Education."

But newly uncovered documents obtained by CNN prove Biden ardently opposed the policy at all levels in the '70s and introduced legislation to ban busing ordered by federal courts, not just busing policies put in place by the Department of Education.

In a 1975 interview, Biden also went much further than just opposing busing policies instituted by the Department of Education, calling it an "asinine concept" and saying, "I've gotten to the point where I think our only recourse to eliminate busing may be a constitutional amendment."

Visit Business Insider's homepage for more stories.

Former Vice President Joe Biden flatly denied he had opposed school busing in a tense exchange with Sen. Kamala Harris during the first round of Democratic primary debates on June 27, but newly uncovered documents obtained by CNN prove he ardently opposed the policy at all levels in the 1970s.

During the second night of debates in Miami, Harris confronted Biden over comments he made recently at a New York City fundraiser fondly reminiscing about the days when he worked with the ardently pro-segregation and actively racist Democratic Sens. James Eastland and Herman Talmadge.

"I was in a caucus with James O. Eastland. He never called me 'boy,' he always called me 'son,'" Biden said, adding, "Well guess what? At least there was some civility. We got things done. We didn't agree on much of anything. We got things done. We got it finished."

Harris, who is of African American and Indian American heritage, took Biden to task over his comments, saying, "I do not believe you are a racist, and I agree with you when you commit yourself to the importance of finding common ground, but it's personal and it was hurtful to hear you talk about the reputations of two United States senators who built their reputations and career on the segregation of race in this country."

Read more: 'It was hurtful to hear you talk': Kamala Harris denounces Joe Biden's work with pro-segregation senators in tense exchange

She then raised the issue of Biden's opposition to busing at the time, saying, "There was a little girl in California who was part of the second class to integrate her public schools, and she was bused to school every day. That little girl was me. So I will tell you that on this subject, it cannot be an intellectual debate among Democrats."

Biden immediately jumped to defend his record, accusing Harris of "mischaracterizing" his comments and emphasizing that he did not intend to "praise" racists, further highlighting his work advancing civil rights throughout his career.

When pushed by Harris as to whether he was wrong in opposing school busing at the time, Biden said: "I did not oppose busing in America. What I opposed is busing ordered by the Department of Education. That's what I opposed."

But in multiple letters from Biden to Eastland and other senators obtained by CNN from Eastland's archives and dated back to 1977, Biden introduced legislation banning busing mandated by federal courts, not just policies ordered by the Department of Education.

In a letter from March of 1977, Biden described the bill as getting to "the heart of the injustice of court-ordered busing," adding, "It prohibits the federal courts from disrupting our educational system in the name of the constitution where there is no evidence that the governmental officials intended to discriminate."

Read more: Joe Biden's dicey past on racial issues could come back to bite him in the 2020 Democratic primaries

In a letter dated June 1977, Biden wrote to Eastland — then the chair of the Senate Judiciary Committee — thanking him for his "efforts in support of my bill to limit court ordered busing." A year later, Biden even invited Eastland to promote his anti-busing legislation on the Senate floor.

CNN and HuffPost reported that Biden made curtailing the use of busing one of his central causes in the Senate, introducing anti-busing legislation and amendments and even voting against historic African American DOJ nominees over the issue.

In a 1975 interview cited by HuffPost, Biden also went much further than just opposing busing policies instituted by the Department of Education, calling it an "asinine concept" and saying, "I've gotten to the point where I think our only recourse to eliminate busing may be a constitutional amendment."

In a statement to CNN, the Biden spokesman Bill Russo reiterated that at the time, Biden believed that government busing policies did not offer "real answers to problems like educational inequities," and further emphasized other parts of Biden's record on civil rights.

"Joe Biden is today — and has been for more than 40 years in public life — one of the strongest and most powerful voices for civil rights in America," Russo said. "His long commitment to civil rights has repeatedly been recognized by many of the most important civil rights organizations in America."

Read more:

Biden took a stunning beating on the debate stage, and now the Democratic primary looks wide open

Kamala Harris was the breakout star of the 2nd night of Democratic debates, outperforming frontrunners Biden and Sanders

Alexandria Ocasio-Cortez condemns Joe Biden for 'waxing nostalgic' about working with racist segregationists

Joe Biden bragged about a harsh 1992 crime bill that did 'everything but hang people for jaywalking'