The Heartless Libertarian has the skinny on just how professionally paranoid the US Secret Service is. I understand that protecting their charges is their #1 job, but good grief. Not that I'd ever be a candidate for POTUS (Hear those skeletons rattling in the closet?), but if I were, I'd rather take my chances than know that something like this was going on in the name of protecting me.
Of course, I'd also be the first POTUS (as far as we know) who would be carrying as a matter of course.