The first female African American U.S. senator is defending former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE after Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.) criticized him for his past opposition to federally mandated busing.

“We can be proud of her nonetheless, but her ambition got it wrong about Joe,” former Sen. Carol Moseley Braun (D-Ill.) told Politico for a story released Sunday. “He is about the best there is; for her to take that tack is sad.”

Moseley Braun has endorsed Biden in the 2020 Democratic primary.

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Harris during last week's primary debate accused Biden of being opposed to busing black students to majority white schools, noting that she personally benefited from such busing.

"There was a little girl in California who was part of the second class to integrate her public schools, and she was bused to school every day," Harris said to Biden. "That little girl was me."

Biden called Harris's criticism a "mischaracterization" of his views and said his issue was with the Department of Education administering busing policies.

The California lawmaker also criticized Biden for saying that there had been "civility" when he worked with segregationist Sens. James Eastland (D-Miss.) and Herman Talmadge (D-Ga.) in the 1970s.

The exchange during the debate was seen a big moment for Harris, who has received a surge of support and donations in its wake.

Moseley Braun's defense of Biden may be crucial in Iowa, an important early caucusing state where the former vice president currently leads in polls.