In a keynote address at Chicago's convention center, Louis Farrakhan recently called the junior senator from Illinois "the hope of the entire world that America can change."
Asked at the Democratic debate in Ohio about Farrakhan's endorsement, Obama said he did not solicit the support of Farrakhan, who has been criticized for saying such things as Judaism is a "gutter religion."
Obama said he's "been very clear" in his denunciation of Farrakhan and his past statements.
"I did not solicit this support," Obama said.
After being pressed by Clinton, who said she unequivocally declined support from a group she described as anti-Semitic when she was running for New York senator, Obama rejected Farrakhan's support.
"I was willing to take that stand," Clinton said. "At the time, I thought it was more important to stand on principle."
Clinton said Obama was not being direct enough, noting "there's a difference between denouncing and rejecting" a supporter's endorsement.
"And I made it very clear that I did not want their support, I rejected it," she said.
Obama responded, saying: "I'm happy to concede the point and I would reject and denounce."