US Vice President Kamala Harris has said President Joe Biden had a "slow start" in his debate with presidential challenger Donald Trump but finished "strong."
"People can debate on style points, but ultimately, this election and who is the president of the United States has to be about substance and the contrast is clear," she told broadcaster CNN, which hosted Thursday's debate.
Harris accused Trump of lying "again and again" during the duel in Atlanta, in the US state of Georgia.
During the testy 90-minute debate, 81-year-old Biden repeatedly hesitated when giving answers, misspoke and did not always answer coherently.
US political analysts branded the incumbent's performance as "painful," saying it has sparked "panic" within his Democratic Party.
