Iowa's effect on the polls is a lot more complicated than people think.
There's not a one-size-fits-all bounce from winning the state. Sometimes the bounce is enormous. Sometimes it's NEGATIVE.
There's not a one-size-fits-all bounce from winning the state. Sometimes the bounce is enormous. Sometimes it's NEGATIVE.
As a rough approximation, the bounce is fairly well-predicted by how much better a candidate does in Iowa than in her national polls. e.g. a candidate polling at 10 percent nationally, who wins Iowa with 30%... she's gonna get a bounce. But that's just a rough approximation.
Are you seen as an underdog/surprise winner? (e.g. did you beat your polls?) Are there mitigating factors? (From a neighboring state? Then your win might be discounted.) How big is your margin? What's the media narrative over the course of the night? All that stuff matters, too.
If you held Iowa *today*, Buttigieg would potentially stand to get a big bounce…although expectations for Buttigieg are rapidly increasing, which could mitigate the bounce. You see how this stuff is circular? There's likely something real to the notion of "peaking too soon".
As for Biden, Warren and Sanders, limping to victory with say, 21% of the vote in IA might not get them much of a bounce since expectations are reasonably high in each case. An emphatic win would help. But finishing in the low teens would hurt. There's more downside than upside.
