Well, there are many questions surrounding the Secret Service, whose main duty is to protect President's past and present. How could agents have failed so woefully in their task with Donald Trump? Congress has launched an investigation into what happened. Here's Ross Atkins.

There's more evidence there were warnings in the minutes before this happened. Those shots were fired at 6:11 PM on Saturday by a man on this roof. He was 130 meters away from the stage where Donald Trump was speaking. The US Homeland Security Secretary has said, a direct line of sight like that to the former President should not occur. But not only was there a direct line of sight, there were warnings about a possible threat. This video has emerged. It's from 1 minute, 45 seconds before the attack. Yeah, look.

There he is.

In this clip, people have noticed a man on a roof. They're shouting to an officer. He's on the roof. He's right here. Right on the roof. It's confirmation some police knew about the threat close to two minutes before the attack. Then this video, filmed by a spectator inside the rally, shows the seconds before the attack. We see a person running, apparently aware there's an issue. That adds to this video, filmed at 6:10 PM, which shows a man and what appears to be a police officer looking at the buildings. And there's this account.

He had a rifle. We could clearly see him with a rifle. And the police were like, Huh? What? They didn't know what was going on.

Given these warnings, in those two minutes, why wasn't Donald Trump taken off stage? Why wasn't the man on the roof challenged? We've now heard from County Sheriff Michael Sloop. His local police were present. He says the attacker was seen outside the rally venue before Trump started speaking and was identified as a suspicious person. He also says the officers didn't know he was armed and that they momentarily lost track of him. Sheriff Sloop also says that later, with the speech underway, an officer checked the roof of this building.

The officer had both hands up on the roof to get up onto the roof, never made it because the shooter had turned towards the officer, and rightfully and smartfully, the officer let go.

Shots were fired at Trump shortly afterwards, the sheriff says. It's not clear how much the Secret Service knew about all of this at the time, but evidence now shows that close to two minutes of clear warnings didn't lead to the attack being stopped.

Rose Atkins, our analysis editor reporting there. Well, Frank Gardner is with us. Frank, you're the security correspondent. What are the burning questions that the Secret Service has to answer in this?

Sure. Well, let's break this down, Clive, into what worked and what didn't. There was a failure to prepare correctly for this venue. The normal protocol would be for the Secret Service to send their agents onto the location well in advance, sometimes weeks in advance, and clear the concentric circles around the VI IP, whether it's a President, former or serving. And extraordinarily, they failed to sanitize that rooftop just 130 meters from where Donald Trump was speaking. A lot of people have said there should have been a secret service sniper detail on that roof because it was a clear area of concern. There was also a failure to process the warnings that you heard there in Ross Atkins' piece. They were being passed to police, to local law enforcement, and in some cases to the Secret Service, and that wasn't being acted on. So somebody was either ignoring it or dismissing it. Now, what did work well was the immediate reaction on stage. You saw it there. Donald Trump had clearly been trained for this. He ducked immediately. Maybe it's an instinct, maybe they trained him for it, but that worked. And the secret service in the immediate surroundings to him bunkered him.

They protected him in a box and got him off stage. A little slowly, but they did that. Meanwhile, something known as Team Hercules, the sniper team, the counter-sniper team, neutralized, in their words, the threat.