Tonight, 24 hours after the alarming assassination attempt on former President Trump, growing questions about what many in law enforcement are calling an enormous security failure.

If that bullet was two inches to the right, it would have penetrated the former president's forehead and we would have a great american tragedy on our hands.

The Secret Service was responsible for security at the rally and tonight is facing an independent review of how the shooting happened. This video shows the alleged shooter on, on a roof just outside the rally's security perimeter, firing shots before he was taken out by a Secret Service counter sniper team. That quick response has been praised as life saving. But former law enforcement officials say the entire incident never should have happened.

The buck does stop with the US Secret Service. It's their plan. You're responsible, so you can't deflect blame on anybody else. And you have to make sure all these layers are put into place.

Former President Trump was speaking from a stage in a field. The shooter was only 148 yards away on top of a roof, one of only a few rooftops in the rural area. A question tonight, why was that rooftop not secured?

So if you look at an aerial shot of that area, maybe there is half a dozen roofs, but there's not thousands of roofs. It could have been covered for a couple hours and it should have been.

Also, witnesses say they saw the gunman and tried to warn police. The question now, were those witnesses ignored?

We're pointing at them. The police are down there running around on the ground. We're like, hey, Mandev, there's guy on the roof with a rifle. And the police are like, huh?

What?

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

Tonight, the Secret Service did not respond to questions from NBC News, but is denying allegations it rebuffed requests from the Trump campaign for more resources.

As for those witness accounts, authorities say they'll investigate. And House Republicans have announced an investigation, too, including calling on the secret service director to testify.

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