Whatever questions come flying at Herman Cain at Tuesday’s night Republican debate in Las Vegas, there is one big one he has to answer: Are you serious? It is a measure of Cain’s success that anyone would care to ask. For much of this year Cain seemed to be enjoying his role as political novelty act — an entertaining sideshow at debates, and even an occasional presence on the early-state campaign trail — when he wasn’t otherwise occupied with speeches, television appearances and book-tour publicity. But now that Cain, buoyed by bulging poll numbers, is demanding to be viewed as...