Former Vice President Joseph R. Biden Jr. said Friday that he had not been prepared for Senator Kamala Harris to so pointedly question his record on school busing during the first Democratic debates, extending the dispute between the two presidential candidates, who have sparred repeatedly in the week since their high-profile confrontation.

In an interview broadcast Friday morning on CNN, Mr. Biden said that while he had expected candidates to target him, he had been caught off guard by Ms. Harris’s criticism in part because of their relationship.

“I was prepared for them to come after me, but I wasn’t prepared for the person coming at me the way she came at me,” Mr. Biden said, adding that Ms. Harris “knows me” and had known his late son, Beau Biden.

Mr. Biden also asserted that Ms. Harris had taken his position on school busing out of context. He reiterated in the CNN interview that while he believed federally mandated busing “did not work,” he was in favor of voluntary local busing efforts to desegregate schools like the one Ms. Harris participated in as a child in Berkeley, Calif., in the 1970s.