A buddy of mine in the Army has a friend who was on the Secret Service detail and he said that bush really is one hell of a runn and that most of the Secret Service guys had trouble pacing him - they would follow in a golf car then switch out those that would jog with him.
Also, so the story goes, down at his ranchin Texas he would make an award that he would hand out to anybody that could keep up with him for his entire run - in the Texas heat. Needless to say, as I was told, not many people were able to do that.