Polls this cycle have been all over the place, yet they consistently show how momentum is derived largely from debate performancesCaution, everyone. All of us who are following the election closely are very much aware of the debates. But that's simply not the only thing going on. Since December, there are ad wars in all of the early primary states, with saturation levels of TV ads, presumably accompanied by other forms of advertising. There are also candidate appearances and local news hits. Each early state has its own local conservative talk radio hosts. And then there's the various nationally syndicated radio hosts, plus Fox News. On top of all that, there's straight news coverage, including on those local news shows and within the GOP-aligned partisan press, of campaign developments including not only debates but also polls and primary results. All of these may produce direct and indirect effects, including pure "momentum" effects when inattentive voters who like all the candidates simply tell pollsters they support the candidate they most recently heard something good about. And of course saying that "debate performances" moved polling numbers is also dicey just by itself; impressions of those performances can be unmediated for those who watch the debates in full and nothing else, or mediated by the press and party actors for those who learn (or remember) what happened from news recaps, sound bites, and whatever pundits and talk show hosts choose to talk about.
Getting back to debates vs. everything else: most of that, to most of us who are not in the state that's preparing for a primary this week, is mostly or entirely invisible. The debates, on the other hand, are extremely visible. Later on, with any luck we'll get some good analysis that can attempt to sort out all these effects. Including why we're getting all these large swings (Nate Silver today suggested the old Mickey Kaus effect; I'm sticking with the "no heavyweight" theory). But for now we should all be very cautious, in my view, about leaping to the conclusion that the most visible thing to us is the one that's pushing all the polling.