Bystander Effect is real. Noone wants to take responsible in the heat of the moment as they subconsciously feel that someone who is better fit to help is already doing so.

The parking lot area where the videos were filmed does not seem to be behind the check point. Therefore someone had to have their sidearm with them. Not saying to take out the shooter like a cowboy, but they could atleast fire off a round into some soft ground as a distraction and hopefully the president would have been removed from sight.