JOHN YANG: Good evening.

I'm John Yang.

It hadn't happened in more than four decades, someone who'd been President of the United States shot in an assassination attempt.

Former President Donald Trump's wounds aren't life threatening.

But last evening shooting in Butler, Pennsylvania could take an already divisive presidential campaign into even more volatile waters.

JOHN YANG (voice-over): It began as a routine seen a swing state campaign rally on a hot summer day but as former President Donald Trump launched into his stump speech, everything changed in an instant.

DONALD TRUMP, Former U.S. President: Take a look at what happened.

JOHN YANG (voice-over): Trump dropped straight down sworn by Secret Service agents.

When agents knew that snipers had shot the gunman they raise Trump to his feet.

The right side of his face bloodied, they hustled him to the safety of an armored SUV.

This morning in the Pittsburgh suburb of Bethel Park, about 50 miles south of the rally site, police and reporters descended all trying to learn what they call it about the man investigators identified as the suspected shooter 20 year old Thomas Matthew Crooks, he was a registered Republican and in 2021, contributed $15 to a liberal voter turnout group.

The FBI is taking the lead in the investigation.

KEVIN ROJEK, Special Agent in Charge, FBI: Again, we're so working through the security apparatus that the Secret Service had in place.

What potentially happened that there's going to be a long investigation into exactly what took place and how the individual is able to get access to the location, what type of weapon he has.

JOHN YANG (voice-over): Official said the shooter was on a nearby rooftop beyond the area, the Secret Service controlled.

The shots killed a man attending the rally and critically wounded to others.

Witnesses describe the chaos.

CHARLES REETY, Eyewitness: All of a sudden it sounds like firecrackers going off.

But then I heard the shots.

And then all of a sudden somebody horrors get down on the ground and everybody's going down on the ground as low as they can get.

SAURABH SHARMA, President, American Moment: Was very clear that someone had been much more seriously injured than the President and there was visible blood everywhere.

JOHN YANG (voice-over): One person said he'd seen the would-be assassin and pointed him out to authorities.

GREG SMITH, Eyewitness: We can clearly see him with a rifle.

Absolutely.

We're pointing at him.

The police are down there running around on the ground.

We're like, hey, man, there's a guy on the roof with a rifle.

And the police are like, huh?

What?

You know, like didn't know what was going on.

JOHN YANG (voice-over): At the White House today, President Biden called for Americans to come together.

JOE BIDEN, U.S. President: There's no place in America for this kind of violence or any violence for that matter.

And assassination attempt is contrary to everything we stand for as a nation, everything.

JOHN YANG (voice-over): A similar call came from House Speaker Mike Johnson on NBC's Today.

REP. MIKE JOHNSON, Speaker of the House: We've got to turn the rhetoric down if you have political opposition and political opponents but we're all Americans and we have to treat one another with dignity and respect.

We can have heated political discourse and debates but it shouldn't be personal and we shouldn't be targeting people.

JOHN YANG (voice-over): The Trump campaign said the former president is fine.

And yesterday as Secret Service agents moved him off stage, his mood was clear.

A clenched fist and the words flight, fight.