Donald Trump called on the United States to ‘stand united’ on Sunday, hours after the former president survived an assassination attempt at a campaign rally in Pennsylvania. The shooting in the town of Butler, north of Pittsburgh, is likely to cause political shockwaves in the United States just months ahead of Trump’s rematch with President Joe Biden in November’s elections. Footage from the scene showed Trump defiantly raising his fist with blood on his face as he was escorted off the stage by US Secret Service agents. A shooter was able to climb to an “elevated position,” a Secret Service s…