‘As we mark the 20th anniversary of the terrible attacks on September 1Earlier, the Bidens joined the Clintons and the Obamas at the New York City ceremony at Ground Zero.At the western Pennsylvania site, Vice President Kamala Harris had called for a ‘united America’ Saturday as she joined former President George W. Bush at the 9/11 memorial ceremony in Shanksville, Pennsylvania, to mark the 20th anniversary of the terror attacks.