When Marginal Candidates Become Competitive Candidates

I've been wondering about the strange staying power of such seemingly marginal candidates for the Republican presidential nomination as Michele Bachmann and Herman Cain. Via Andrew comes this observation from Daniel Larison:

At what point are we going to start acknowledging that the national and local polls are telling us that it is Pawlenty and Huntsman that are the clearly marginal candidates, and Paul, Bachmann, Cain, and even the ridiculous Gingrich are the competitive ones?