Was Biden's debate performance against Trump the only reason for his exit? What Harris said

Vice President Kamala Harris once again staunchly defended President Joe Biden's mental fitness when questioned about his capability to lead. In a recent NBC News interview, Harris was pressed on whether she had been honest with the American people regarding her observations of Biden's performance during his debate with Donald Trump.
“It was a bad debate” Harris acknowledged but insisted that "people have bad debates". When asked if the President's debate performance was a factor in his decision not to run for re-election, Harris responded, "You’d have to ask him if that’s the only reason why."

The interview with Hallie Jackson took place against a backdrop of growing unease among voters regarding the state of the economy, with a recent NBC News poll revealing that a majority believe Biden's policies have negatively impacted their lives. In response to whether the past four years might hinder her presidential campaign, Harris clarified, “Mine will not be a continuation of the Biden administration,” promising to bring her own ideas and experiences to the forefront.
"I bring my own experiences, my own ideas to it, and it has informed a number of my areas of focus, most of which are on, to your point, lowering costs. So part of my plan includes what we need to do to bring down the price of groceries," she said.
This is not the first time that Harris has faced questions about Biden's mental fitness, earlier, in a more contentious exchange with Fox News' Bret Baier, Harris also defended Biden against allegations of cognitive decline. “I have watched from the Oval Office to the Situation Room, and he has the judgement and experience to make very important decisions,” she asserted. Harris pointed out that Biden is not the one running for re-election, saying, “Joe Biden is not on the ballot,” and shifted focus to concerns about former President Donald Trump, asserting, “He’s not stable.”
Harris' support has seen a decline in recent weeks, with a Reuters/Ipsos poll showing Harris leading Trump by a slim margin of 46% to 43%, yet highlights a troubled electorate with a significant portion feeling the country is on the wrong track. Voter sentiment reflects widespread discontent, with 70% indicating that the cost of living is deteriorating and 60% believing the economy is heading in the wrong direction.