US President Joe Biden on Thursday introduced Ukrainian President Volodymyr Zelensky as “President Putin” in a speech at a NATO summit in Washington. “And now I hand over to the president of Ukraine, who has as much courage as he has determination – ladies and gentlemen, President Putin,” Biden said. Biden corrected himself a moment later, adding: “….to beat President Putin – President Zelensky!” The apparent slip-of-the-tongue came at a time when US politics is becoming increasingly dominated by concerns about the 81-year-old president’s mental capacity. His performance is being watched clo…