I want to be clear that this analysis of Virginia represents a case study, rather than a prediction, of how Iowa will turn out. A gaffe swinging the balance in a race is more the exception than the rule. The reason why Allen’s comment mattered in Virginia had to do with three major factors, in my view.

First, the race was on the fringe of being competitive before the gaffe. Webb’s campaign wasn’t a lost cause, but Allen was not an easy target, even in a Democratic-leaning environment. Webb probably needed some catalyst to generate more attention for his race and push him over the finish line.

Second, the news media found other examples of intemperate or insensitive remarks by Allen, which gave the story life and made it a prism for interpreting the campaign.

Third, the gaffe helped to mobilize the Democratic base around Webb’s campaign. Although Webb was already a favorite of the netroots, Allen’s comment dramatically increased their attention on Virginia. And the netroots maintained their heightened attention right up through the November election.

I’d argue that the first condition is replicated in Iowa.