Law based White House leader Joe Biden went under savage assault for his record on race in a broadcast banter with nine opponents on Thursday.
Representative Kamala Harris raised his past work with narrow-minded congresspersons, and his past restriction to an arrangement battling isolation in schools.
He said she had "mischaracterised" his position, demanding he had entered governmental issues to support social equality.
The hopefuls are competing to take on Republican President Donald Trump.
Firecrackers likewise flew in the primary discussion with 10 different contenders on Wednesday.
The Democratic hopeful will be picked at the gathering's show the following summer, before the person in question faces Mr Trump in the November 2020 decision.
