The FiveThirtyEight Team Goes To Iowa

Like so much else at this point in the campaign, Wednesday morning’s Des Moines Register/Bloomberg Politics Iowa poll could be looked at in either of two ways for the leading candidates. For Ted Cruz, the glass-half-full interpretation is that the best poll in the state still shows him ahead — by 3 points over Donald Trump — when several other recent polls in Iowa had shown a narrow advantage for Trump instead. The glass-half-empty interpretation is that Cruz’s lead is diminished: The previous DMR/Bloomberg poll, taken a month ago, had Cruz ahead by 10 points instead. I’m not sure which case I find more persuasive, but here’s a fuller breakdown of the arguments.

DES MOINES — The new Des Moines Register poll for the Republican Iowa caucuses conducted by Ann Selzer is out, and this race is what we thought it was. The survey, conducted from Jan. 7 through Jan. 10, finds Ted Cruz leading Donald Trump 25 percent to 22 percent with Marco Rubio in third with 12 percent. The poll barely moved the FiveThirtyEight forecasts. In our polls-only forecast, Ted Cruz and Donald Trump are about even; we give Cruz a 42 percent chance of winning and Trump a 40 percent chance. Each had a 42 percent chance before the new poll. Rubio is well back at only a 10 percent chance, while no other candidate has a better than 5 percent chance. Our polls-plus forecast is also holding fairly steady. Cruz is up to 50 percent from 49 percent yesterday. Trump is down to 26 percent from 28 percent, and Rubio is down to 17 percent from 18 percent. Again, no other GOP candidate has a better than 5 percent chance of winning the caucuses in this forecast. Compared to the polls-only forecast, the gains for Cruz and Rubio in the polls-plus forecast jibe with the results from Selzer’s poll. Both have net favorability ratings of +50 percentage points or better, suggesting they have more room to grow, while Trump’s net favorability rating is +9 percentage points, suggesting he may be close to maxing out his support. Indeed, it’s the voters who look a lot more likely to back Rubio than to back Trump who say they haven’t fully made up their minds. Voters who say they haven’t decided or could change their vote tend not to be tea partiers, are college-educated or better and are earning $70,000 a year or more in household income. The bottom line: Iowa Republicans have a lot of room to change their minds with a little less than three weeks to go before the caucuses.

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