As he headed towards a confrontation with Kamala Harris in South Carolina this weekend, Joe Biden took an unfamiliar step: he apologised for remarks about work with segregationist senators which attracted criticism for alleged racial insensitivity.

In remarks at a campaign event in Sumter, South Carolina reported by NBC News, Biden said: “Was I wrong a few weeks ago to somehow give the impression to people that I was praising those men who I successfully opposed time and again? Yes I was. I regret it. I’m sorry for any of the pain or misconception.”

The former vice-president, 76, was attacked by other Democratic candidates including Harris and the New Jersey senator Cory Booker, who are African American, after he discussed working with “civility” with two racist Democrats, James Eastland of Mississippi and Herman E Talmadge of Georgia.

On Saturday, he asked: “Should that misstep define 50 years of my record for fighting for civil rights and racial justice in this country? I hope not. I don’t think so.”

Biden has been reluctant to apologize when apologies have been demanded by opponents and activists on issues including his attitude to race and his behaviour towards women.

His wide lead in early polls of the huge Democratic primary field, largely based on name recognition, has been whittled away.

In the RealClearPolitics.com national polling average, the former vice-president now leads by 11 points from Harris. The California senator has passed the Vermont senator Bernie Sanders since the first debates, in which she made headlines with an attack on Biden over his past opposition to federally mandated bussing of students, a way to integrate schools.

On Saturday Biden, a former Delaware senator who has decades-long political relationships in the south, was beginning a swing through South Carolina featuring visits to Sumter, Orangeburg and Charleston.

On his third trip to the state since he entered the race in late April, he stressed the eight years he served with Barack Obama, the first black president, and the significant change for the good he said has taken place in the country since the 1970s.

“I’ve worked to make that change happen, and yes, I’ve changed also,” Biden said in prepared remarks released to the press ahead of his Sumter stop.

Harris was in New Orleans at the Essence festival, where she was among several 2020 White House candidates at the largest annual gathering of black women.

She proposed $100bn in federal grants to help close what she says is a racial wealth gap and address historical discrimination in homeownership against black families.

Announcing her plan, Harris said: “By taking these challenges on, we can close that gap. That not only lifts up black America, that lifts up all of America.”

Harris said the plan would help at least 4 million families living in areas that were redlined, a segregation-era practice that limited black borrowers’ ability to buy homes and set boundaries on where they could live, affecting the wealth of those families for generations.

Harris’ plan would address federal policy on how credit scores are calculated to include payments made on rent, telephone bills and other utilities, in order to increase credit access for minority borrowers.

She was due to move on to South Carolina, where she and Biden could expect to be pressed on their tense debate exchange.

The South Carolina primary is more than seven months away but Biden and Harris appear destined for a showdown there, their campaigns banking on the backing of black voters.

Several Harris supporters in the state have said her attack on Biden struck a chord. Marguerite Willis, a recent Democratic candidate for governor, said when Harris spoke in the debate about her own experiences being bussed as a child, the entire room grew quiet.

“Growing up here in South Carolina, that’s meaningful to us,” she said. Schools were segregated when she was a kid and she recalled not meeting a black girl her age until leaving for college. “So when she talked about being bussed, it was powerful for me and I’m sure it’s powerful for a lot of people here who have experiences of their own.”

Harris planned to appear in Florence, Hartsville and Myrtle Beach in her ninth trip to South Carolina, having spent more time there than any other state.

In the Miami debate, Harris was unrelenting in her criticism of Biden, both for his views on bussing and the comments he made about segregationists. Biden told CNN in an interview aired on Friday that he “wasn’t prepared for the person coming at me the way she came at me” and noted that Harris knows him and his son, Beau, who died of brain cancer in 2015.

Ahead of his South Carolina stops, Biden’s campaign said he planned to say his lengthy public service career “will be weaponized against him by opposition researchers”, would pledge to “take on those attacks directly” and would not allow his record “to be distorted and mischaracterized”.

The state senator Dick Harpootlian, backing Biden, said he had heard from some voters that they felt Harris’s debate attack was “disrespectful”.

“I think it resonates with younger voters who get all their news off Twitter or Facebook. It’s an echo chamber,” Harpootlian said, adding that he believes the state’s primary voters will be older and heavily African American. “Those are Biden’s guys, his men and women ... They want to know what they’re getting. They don’t want a promise of what’s to come in the future.

“She can’t build herself solely on tearing Joe Biden down. She took that shot. What’s she offering?”