Ms Jackson asked Harris if she had been honest about Biden when she endorsed his re-election bid.
“You never saw anything like what happened at the debate night behind closed doors with him?” Ms Jackson asked.
“It was a bad debate. People have bad debates,” Harris replied, referring to the face-off between Trump and Biden in June.
Ms Jackson then followed up, saying Biden’s poor debate performance was the reason Harris is now the Democratic party’s nominee.
“Well, you’d have to ask him if that’s the only reason why (he stood down),” Harris said.
Ms Jackson again asked about Biden.
“I am running for president of the United States. Joe Biden is not – and my presidency will be about bringing a new generation of leadership to America,” Harris said.
She then vouched for the president’s political achievements and leadership.
“I speak with not only sincerity, but with a real, first-hand account of watching him do this work. I have no reluctance of saying that,” she said.