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Who’s Winning Iowa And New Hampshire?

We launched our forecasts for the Iowa caucuses and New Hampshire primaries today. For much more detail about how this all works, you can read here. But our premise is that, given the challenges inherent in predicting the primaries, we’ll be publishing two models instead of pretending we’ve found a magic bullet:

  • The first model, which we call polls-only, is based only on polls from one particular state. (Iowa polls in the case of Iowa, for example.) It’s basically an updated version of the model we used for the primaries four years ago.
  • The second model, polls-plus, also considers endorsements and national polls, in addition to state polls, and tries to consider the effect that Iowa and New Hampshire could have on subsequent state contests. (National polls aren’t necessarily a positive for a candidate in the polls-plus model; instead, it’s a bearish indicator when a candidate’s state polls trail his national numbers.)

Historically, polls-plus would have been somewhat more accurate, but it’s pretty close — so we think the models are most useful when looked at together. Indeed, they present different perspectives on the races this year, mostly because of that endorsements variable, which helps Hillary Clinton and Marco Rubio but hurts Bernie Sanders and Donald Trump. If you take a strictly empirical view of the primaries, accounting for the establishment’s historical tendency to win out in the end, you’ll probably prefer the polls-plus model. If you think “this time is different” — or you’re a Trump or a Bernie fan — you’ll probably like polls-only instead.

Let’s go through the four races we’re forecasting so far:

Iowa Republicans. Before the new year, Ted Cruz appeared to have a narrow polling lead over Trump, but that’s less clear now, with several recent polls showing a small advantage for Trump instead. In fact, the polls-only forecast now has the race as a dead heat, giving both Trump and Cruz a 42 percent chance of winning Iowa.

Cruz retains an edge in the polls-plus forecast, however; it likes him because his Iowa polls exceed his national polls (while the opposite is true for Trump). Polls-plus gives Cruz a 49 percent chance of winning Iowa, to Trump’s 28 percent.

What about an upset in Iowa? Given how volatile the polls can be there, it’s too soon to completely write off third-placed Rubio. He has an 18 percent chance of winning Iowa according to polls-plus and a 9 percent chance based on polls-only. Other candidates, however — including Ben Carson, who is sinking so much that he’s at risk of dropping out, according to the model — are true long shots.

Iowa Democrats. Because public opinion can shift rapidly in the primaries, our models put a lot of emphasis on the most recent polls. That’s good news for Sanders, who has been neck and neck with Clinton in Iowa polls published this month after trailing her for most of last year. In fact, the race is nearly a tossup: He now has a 45 percent chance of winning Iowa according to polls-only, although the polls-plus model, noting Clinton’s dominance in endorsements, is more skeptical of Sanders, giving him a 27 percent chance instead.

New Hampshire Republicans. Of the four races we’re forecasting right now, this one is probably the most interesting, even though it also features the clearest leader: Trump, who has led almost every New Hampshire poll since July.

Let’s start with the good news for Trump. Not only is he leading — he’s also gained a bit in the latest New Hampshire polls, polling at about 30 percent recently, compared with 26 percent in December.

Nonetheless, it’s early in New Hampshire, and there are five other candidates besides Trump who have at least a semi-credible path to victory there. Thus, recognizing the uncertainty in the race, the polls-only model has Trump with a 55 percent chance to win the state: pretty good, but still barely better than a coin flip.

The polls-plus model also has Trump as the front-runner but puts his chances lower, at 39 percent, in part because it gives decent odds to a number of candidates from the moderate and establishment parts of the GOP. Collectively, Rubio, John Kasich, Chris Christie and Jeb Bush have a 47 percent chance of winning New Hampshire. Among that group, Rubio has the best chance (23 percent), while Kasich’s fortunes (11 percent) have been rising. Bush’s chances are just 6 percent, on the other hand, and have continued to fall.

It’s also conceivable that Cruz could win New Hampshire, especially after a big win in Iowa.

New Hampshire Democrats. Here, there’s a split between the models. Sanders is a 73 percent favorite according to polls-only, while polls-plus — noting Clinton’s advantage in endorsements and that she’s favored in Iowa — gives Clinton the slightest edge, with a 53 percent chance to Sanders’s 47 percent. Essentially, she’d be following the path that Al Gore took over Bill Bradley in 2000, when an Iowa victory propelled him to a narrow victory in the Granite State. But the polls-plus model is designed to lower the effect of the endorsements variable to zero by election day in each state. So if Clinton keeps falling in New Hampshire and Iowa polls instead of rising, the establishment may not be able to bail her out, and she’ll have to contemplate the possibility of being swept in both states.

Forecasts will be coming soon in other states like South Carolina once more polling becomes available in them.

Check our our live coverage of the Republican debate.

Nate Silver is the founder and editor in chief of FiveThirtyEight.