The most consequential poll in politics is about to be released

The hype surrounding this year’s pre-caucus poll is palpable, and for good reason. The Des Moines Register/CNN/Medicom survey of likely Iowa Democratic caucus-goers doesn’t only capture the state of play in the all-important first voting state. It has the power to fuel a candidate’s 11th-hour momentum — or damage a contender who under-performs expectations. J. Ann Selzer, the Iowa-based pollster who has worked for the Register for decades, is a minor celebrity in politics and widely regarded as one of the top survey researchers in the country.

And because the race is so close and crowded — the previous Des Moines Register/CNN/Mediacom poll showed the top four candidates separated by only 6 points — the planned release at 8 p.m. Central Time will have political operatives and observers glued to their TV screens and frantically refreshing their web browsers.

But not so fast, pollsters say: Even Selzer’s gold-plated poll shouldn’t be taken as gospel for what is going to happen on Monday night. That’s because, in addition to all the pitfalls that face pollsters around turnout and the composition of a primary electorate, caucuses present their own unique challenges.