If you’re interested in how undecideds vote, then go to this old FR thread and then go to like for the full article
http://www.freerepublic.com/focus/f-news/2879506/posts
Secondly, Nate Silver -- much like Frank Rich -- is a math-impaired idiot who couldn't get serious employment elsewhere. (see also, Frank Rich's current gig)
Thirdly, most importantly, the unique symmetry of the Incumbent Rule (Panagakis, Bowers, et al) is that the corollary has held true for Presidential elections, and nothing else. An Acceptable Challenger will take at least 80% of the Undecideds from a sitting President.