Of course, neither Gephardt nor Giuliani won Iowa, and there’s still reason for caution. Throwing Walker’s polling average (18.4 percent) into a logit model with past early leaders indicates that Walker has only a 4 percent chance of winning the caucus. Realistically, his chances are almost certainly higher than that, yet none of the four Iowa caucus survey leaders polling at less than 30 percent at this point have gone on to win the caucus.

Unlike those eventual losers, however, Walker isn’t well known. In the latest live interview poll, conducted by Quinnipiac, 36 percent of Iowa caucusgoers could not form an opinion of Walker. Only 15 percent of Democrats couldn’t form an opinion of Gephardt in April 2003. Five percent of Republicans (paywall) had no opinion on Giuliani in May 2007. And 3 percent of Democrats (paywall) and 10 percent of Republicans (paywall) had no opinion on John Edwards and Romney, respectively. In other words, Edwards, Gephardt, Giuliani and Romney’s leads were more a function of high name recognition than Walker’s, which means Walker has a better chance than those candidates to expand his lead.

Needless to say, a Walker win in Iowa would be a big deal. While it likely wouldn’t eliminate Bush, it would make things very difficult for other conservative candidates to find a foothold going into the more moderate state of New Hampshire. Even though Iowa often doesn’t pick the nominee, no candidate has ever won a party’s nomination after coming in lower than tied for third place in the Iowa caucus.