The glass-half-empty case against Ted Cruz

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.

Our Iowa Republican forecast model splits the difference between these two hypotheses, with Cruz’s position essentially unchanged from where it was before the new poll.

And yet, in the conventional wisdom about who’s going to win Iowa, there’s a lot of glass-half-fullism for Cruz. The prediction market Betfair puts his chances of a win at 65 percent. By contrast, the polls-plus version of our forecast, which accounts for endorsements and the candidate’s standing in national polls in addition to state polls, puts Cruz’s chances at 50 percent (as compared to 26 percent for Trump and 17 percent for Marco Rubio). The polls-only version of our forecast puts Cruz’s chances at 42 percent, essentially tied with Trump.