Ahead of his make-or-break post-NATO press conference Thursday evening, President Joe Biden mistakenly referred to Volodymyr Zelenskyy as “President Putin,” as Democrats call for him to step down amid concerns over his fitness to serve another term. The unforgettable fumble at the NATO event earlier in the day was met by audible gasps in the room, according to the Associated Press. Biden, 81, was at the podium announcing a compact that would unite NATO allies in Ukraine’s war against Russia, when the major flub occurred. After referring to Zelenskyy as “President Putin,” Biden quickly added: “…