Donald Trump has been shot and injured in an assassination attempt at a campaign rally, which saw a spectator and the gunman killed.
The former president escaped with a bullet wound to his ear in the attack, which happened early on Saturday evening as the former president was giving a speech to supporters in Butler, Pennsylvania, about 30 miles (50 km) north of Pittsburgh.
Trump assassination attempt latest
The Republican challenger, who is due to receive his party's formal nomination in Wisconsin this week, has since said it was "God alone who prevented the unthinkable from happening".
Mr Trump was seen ducking to the ground as a series of shots rang out and people screamed in panic during the attack.
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He was mobbed by Secret Service seeking to shield him and as he was bundled off stage to a waiting armoured vehicle with a bloodied ear, Mr Trump pumped his fist in the air in a show of defiance and shouted "fight" as the cheering audience chanted "USA".
As well as one person in the crowd being killed, two people were critically injured after the gunman fired "multiple shots" from an "elevated position" from outside the rally venue, said the Secret Service.
The FBI has named the attack - shot dead by security forces - as 20-year-old Thomas Matthew Crooks, who according to state records was a registered Republican.
Footage at the scene showed a white-roofed factory building, about 150m from where Mr Trump was speaking, with a body and a semiautomatic rifle on top.
Writing on his Truth Social platform, the 78-year-old wrote: "Thank you to everyone for your thoughts and prayers yesterday, as it was God alone who prevented the unthinkable from happening.
"We will fear not, but instead remain resilient in our faith and defiant in the face of wickedness.
"Our love goes out to the other victims and their families. We pray for the recovery of those who were wounded, and hold in our hearts the memory of the citizen who was so horribly killed.
"In this moment, it is more important than ever that we stand united, and show our true character as Americans, remaining strong and determined, and not allowing evil to win.
"I truly love our country, and love you all, and look forward to speaking to our great nation this week from Wisconsin.
Read more:
'Pop pop pop' - Witnesses describe moment of shooting
In pictures: Gunman fires multiple shots at Trump rally
The attack was the most serious attempt to assassinate a president or presidential candidate since Ronald Reagan was shot in 1981.
It has realised concerns about political violence in a deeply divided US less than four months before the presidential election.
Security is being reviewed for the the Republican National Convention, which kicks off in Milwaukee, Wisconsin, on
Monday.
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President Joe Biden,who spoke to his White House rival following the attack, condemned the shooting and said there was "no place in America for this kind of violence".
In an address to the nation he said: "It's sick. Sick.
"We cannot allow for this to be happening."
Trump assassination bid is chance for political reset
James Matthews
US correspondent
The first questions are all about the incident itself, of course - the perpetrator, the motivation and method. Not forgetting: how on earth could this have happened?
It's scarcely believable for anyone who has attended a Trump event and witnessed the security firewall that separates the man from the masses. The agents charged with Donald Trump's protection, Secret Service or otherwise, face a grilling on a failure in the fundamentals of the job.
Allowing a former and, possibly, future president to be caught in the cross-hairs of a sniper's bullet puts them in the firing line and they will have to account for actions that ended in fatality, albeit not of the prime target.
In the wake of the shooting, one eyewitness told the media microphones he was surprised it hadn't happened before now. He's not alone in a country that feels the persistent undercurrent of political violence.
Read the rest of James's analysis
The Biden campaign said it was pausing all messaging to supporters and moving to pull all of its television ads as quickly as possible.
Read more:
'Fundamental security failure' allowed attack, experts say
Minute by minute - how the assassination attempt unfolded
Many Republicans quickly sought to blame the violence on Mr Biden and his allies, arguing that attacks on Mr Trump as a threat to democracy had created a toxic environment.
They highlighted a comment Mr Biden made to donors on 8 July, saying "it's time to put Trump in the bullseye".
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Most opinion polls show the two challengers locked in close contest.
Market investors said the attack and Mr Trump's defiant response would likely increase his chances of winning back the presidency, and trades betting on his victory will grow in the coming week.
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Former president Barack Obama wrote on X: "There is absolutely no place for political violence in our democracy.
"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.
"Michelle and I are wishing him a quick recovery."
His predecessor George W Bush described the shooting as a "cowardly attack" on Mr Trump's life.
