(AP photo)

WASHINGTON (AP) — Kamala Harris spoke slowly but bluntly as she stared at Joe Biden, then began treating him as a hostile witness.

The former prosecutor turned California senator started by saying she didn't think the former vice president "was a racist." But she criticized him for recently "defending segregationists" in the Senate and for once opposing mandatory busing of students to desegregated public schools.

Harris described a young girl in the 1970s who boarded such buses before dramatically offering, "That little girl was me."

The moment was as powerful as it was unexpected, a searing line of attack against Biden, who served as vice president to the first black president. Biden entered back-to-back nights of Democratic presidential debates in Miami as the leading Democratic candidate. Harris showed promise but had not made much of a mark lately.

That changed Thursday.

That Harris and other Democratic presidential hopefuls would come out swinging against Biden was no surprise, and her verbal strike was hardly spontaneous. Moments after the exchange, her campaign tweeted a picture of a school-age Harris with pigtails, over the caption: "There was a little girl in California who was bussed to school. That little girl was me."

In deeply personal tones, Harris hammered Biden for policy choices that she suggested betrayed the spirit of the civil rights movement, if not directly opposing all it stood for. Then she really hit her stride, exhibiting the controlled force of a practiced cross-examiner.

"Do you agree today that you were wrong to oppose busing in America?" Harris asked.

A visibly angry Biden responded that his record was mischaracterized. But he was left denying Harris' comments on a technicality, saying he didn't oppose public school busing, just it being ordered by the Department of Education — decrying federal intervention on the issue on behalf of states.

Harris shot back, "There are moments in history where states fail to support the civil rights of people."

Biden offered only curt responses after that and was so flustered that he failed to lean on his time as Barack Obama's vice president — seeming unsure of himself for prolonged stretches on national television.

Harris said on Friday that the back-and-forth with Biden was her "just speaking truth." She told CBS that she has a "great deal of respect" for Biden and would make no judgment on whether his response was disqualifying.

"That's a decision for the voters to make," Harris said on "CBS This Morning."

Senior advisers to Biden insisted afterward that they weren't surprised by the confrontation with Harris and were satisfied with his response in the time allowed. They noted that while he dismissed Harris' characterization of his relationship with segregationist senators in his early years in the Senate more than 45 years ago, Biden appeared to be listening while she criticized his position on busing.

"I thought it was an important moment. He listened. And you don't judge other people's pain," said Cedric Richmond, Biden's campaign chairman.