The attack, by a shooter who law enforcement officials say was then killed by the Secret Service, was the most serious attempt to assassinate a president or presidential candidate since Ronald Reagan was shot in 1981.

It comes amid a deeply polarized political atmosphere, just four months from the presidential elections and days before Trump is to be officially named the Republican nominee at his party’s convention.

The heavily armed tactical team travels everywhere with the president and major party nominees and is meant to confront any active threats while other agents focus on safeguarding and evacuating the person at the center of protection.

Law enforcement recovered an AR-style rifle at the scene, according to a third person familiar with the matter who spoke on condition of anonymity to discuss the ongoing investigation.

“Everybody went to their knees or their prone position, because we all knew, everyone becoming aware of the fact this was gunfire,” said Dave McCormick, the Republican candidate for U.S. Senate in Pennsylvania, who was sitting to Trump’s right on stage.

Two firefighters from nearby Steubenville, Ohio, who were at the rally told the AP that they helped people who appeared injured and heard bullets hitting broadcast speakers.

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