The FBI recently released technical specifics of the Trump assassination attempt. Let's assume the technical facts aren't a lie and that Crooks used an AEMS red dot scope...

AEMS Red-Holosun

Red dot scopes are designed for fast engagement at 100 yards or less, not for accuracy. The red dot imposes a margin of error because the dot overlays the target. A larger dot = faster acquisition = less accuracy. The AEMS scope is rated at 2 Minute-Of-Angle (MOA), a 2 inch margin of error at 100 yards and almost 3 inches at 140 yards (the distance from Crooks to Trump). The DPMS rifle has a 1 MOA margin of error. The two margin of errors aren't exactly additive but they are cumulative.

Crook's inappropriate combo had a 3+ inch margin of error and is quite possibly why Trump survived.