> …how about a little gangster action duck and put his pistol over the edge and blast the little creep? <
The cop had maybe a 10% chance of hitting rifle guy that way. But it was still the correct thing to do!
One, the gunfire would have alerted everybody and his brother.
And two, it would have shaken up rifle guy. It’s hard to concentrate on taking a long shot when someone off to the side is shooting at you.
The cop had many options, your suggestion and others. But he evidently did nothing. Nothing at all.
From the back of the building towards the shooter is still shooting toward Trump and the crowd. If he'd have missed, he'd be endangering everyone down range.