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The 78-year-old leader was seen ducking on the podium as rapid shots rang out at the rally. He was quickly surrounded by Secret Service agents who escorted him off the stage. The Republican nominee was seen raising his fist and mouthing "fight, fight" as he was whisked off the stage.
The Secret Service, a law enforcement agency that protects US political leaders, said that multiple shots were fired from an "elevated position" outside the rally venue.
"I think that's something that we're going to have to figure out how he got there," Butler County district attorney Richard Goldinger told news agency AFP.
According to local media, the suspected shooter has died. "Butler County District Attorney Richard Goldinger said two people are dead, including an apparent shooter," The Washington Post said. One spectator died from injuries at a hospital while two others are in a critical condition.
Taking to Truth Social, a social media company owned by Trump, the former US president said he was "shot with a bullet that pierced the upper part of my right ear."
"I knew immediately that something was wrong in that I heard a whizzing sound, shots, and immediately felt the bullet ripping through the skin," he said.
The attack has united US political leaders on both sides the spectrum with Trump's rival and US President Joe Biden condemning the attack, saying there was "no place in America for this kind of violence".
"It's sick. It's one of the reasons why we have to unite this country... We cannot be like this, we cannot condone this. The idea that there's political violence, or violence in America like this, is just unheard of. It's just not appropriate. Everybody, everybody must condemn it," he said, adding that he will speak to Trump shortly.
Former presidents Barack Obama and George W Bush have also slammed the "cowardly" attack.
"Although we don't yet know exactly what happened, we should all be relieved that former President Trump wasn't seriously hurt, and use this moment to recommit ourselves to civility and respect in our politics," Obama said.
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