Ukrainian President Voldomyr Zelenskyy and President Joe Biden shake hands in June 2024.Anadolu via Getty ImagesPresident Joe Biden had a major mix-up while speaking at a NATO summit on Thursday.The 81-year-old president introduced Voldomyr Zelenskyy as Vladimir Putin.Biden quickly corrected himself and told Zelenskyy he was "better" than Putin. President Joe Biden introduced Ukrainian President Voldomyr Zelenskyy as Russian President Vladimir Putin in a cringeworthy moment at a NATO conference on Thursday.The inaccurate introduction is Biden's most recent flub amid increasing skepticism over the 81-year-old president's fitness for office, including from members of his own party."Now I want to hand it over to the president of Ukraine, who has as much courage as he has determination," Biden said.