NEW JERSEY – Donald Trump called on Americans Sunday to stand united after he was injured in an assassination attempt – a shocking incident that opened a dark new chapter in an already polarized US presidential race.The 78-year-old former president was hit in the ear at a campaign rally in Butler, Pennsylvania, while the shooter and a bystander were killed and two spectators critically injured in the worst act of US political violence in decades.”In this moment, it is more important than ever that we stand United,” Trump said in a statement on his Truth Social network, adding that…