Democratic presidential candidate Joe Biden has refused to apologise for reminiscing on his work with two long-dead racist senators.
But amid a firestorm of criticism, the ex-US vice-president said he had “detested” the views of late senators who favoured racial segregation.
His rivals have blasted him for saying working with “civility” with the segregationists had “got things done”.
It is the ugliest row so far in this Democratic race for the White House.
Mr Biden is still recovering from similar backlashes that led him to reverse course on federal funding for abortions and praising US Vice-President Mike Penceas a “decent” person.
How did Biden land in trouble again?
The latest row began on Tuesday night when Mr Biden fondly recalled his working relationship after joining the Senate in the 1970s with two southern Democratic senators, Mississippi’s James Eastland and Georgia’s Herman Talmadge.
Mr Biden, 76, said at a fundraiser in New York City that Talmadge had called him “son” but never “boy”, referring to how racist whites addressed black men at the time.
“At least there was some civility,” he said. “We got things done.”
Some of his rivals who are vying to be the Democratic party nominee for the November 2020 presidential election, including Senator Cory Booker, pounced on his remarks.
But the former US vice-president, who is currently leading opinion polls, fought back on Wednesday night.
“They know better,” Mr Biden told reporters while attending fundraisers in the Washington DC suburbs.
“Apologise for what? Cory should apologise. He knows better.
“There’s not a racist bone in my body; I’ve been involved in civil rights my whole career. Period. Period. Period.”
Mr Biden said of the segregationists: “We, in fact, detested what they stood for in terms of segregation and all the rest.”
Biden advisor Anita Dunn told MSNBC: “It’s a story he’s told many times.
“And the point of the story is that you have to be able to work with people, even if they hold positions repugnant to you, in order to make some progress.”