Not likely to help presidential security, (by the time it was deployed the attack would likely be over) although it could endanger hundreds of innocent flag-waving, baby-holding civilians. It might be of some value in fighting off an aerial attack, or a rogue helicopter, but how likely is that? And does it have the fire control capability that would require? All the firepower in the world isn't going to help if it is in the hands of one disoriented, overly excited guy who has just poked his head up through the roof of a violently maneuvering SUV.

Much more effective at protecting The First Dude would be to replace the minigun in that car with a half-dozen marksmen with carbines. On foot, forming a perimeter or a defensive line, 6 guns, 6 walky-talkies, 12 eyes and ears, all mobile and independent but coordinated and cooperating. But of course, it wouldn't be as "cool".