In a literary sense, it seems to me that "ghost stories" only work if there is a plausible explanation for the ghost.
                Say, for instance, the ghost of Ronald Reagan comes back and steals all of the presents out from under some family's Christmas tree. That makes perfectly good sense. But say the ghost of Franklin Roosevelt comes back, and the audience is waiting for something bad to happen. Of course, it never does. A ghost can't really die so things continue on undisturbed, and everybody begins to wonder what all the fuss is about.