Kamala Harris was left aghast when President Joe Biden donned a “Trump 2024” cap at a Pennsylvania firehouse in a bizarre scene at the height of last year’s presidential race, a bombshell new book has revealed. During a visit to a Shanksville firehouse while commemorating the 23rd anniversary of the 9/11 attacks, Biden, now 82, posed with more than a dozen youngsters clad in pro-Trump attire — then briefly put on the cap after being egged on by a member of the crowd. “What is he doing?” Harris — by that point the Democratic nominee after Biden ended his re-election...