US President Joe Biden delivered his speech at a ceremony to mark NATO’s 75th anniversary in Washington in front of the world on Tuesday with no slip-ups and only minor slurring, albeit with close reliance on a teleprompter. Questions surrounding Biden’s mental fitness for office loom over the summit, as the US presidential race heats up between the president and his predecessor, long-time NATO critic Donald Trump. A live televised debate a week and a half ago reignited concerns, including among Biden’s own Democratic Party, about whether he was too frail to lead. As usual at such events, Bide…