Since July, every single poll of the GOP race in Iowa has shown one of two leaders: Donald Trump or Ben Carson.

Every single poll until this week, that is.

Two new polls — from Bloomberg / Des Moines Register, and from Monmouth University, now show Ted Cruz surging into first place. The former (released Saturday), shows Cruz topping Trump by 10 points, while the latter (released earlier this week) shows Cruz up by five.

However, a third poll released earlier this week, from CNN/ORC, shows Trump 13 points ahead of Cruz — one of his largest leads ever in Iowa. So there's some dispute about who's winning.

But the commonality from these and other recent polls is that Cruz is on the rise, and apparently fast picking up support from the free-falling Ben Carson. So Cruz is looking more and more like a serious threat to Trump in Iowa.

A Cruz surge in Iowa makes sense. But will it last?

Politicos have long expected that Iowa could be fertile ground for the Cruz campaign — and troublesome for Donald Trump.

That's because in both 2008 and 2012, 57 percent or more of GOP caucus-goers described themselves as evangelical or born again, according to entrance polls. These evangelical voters helped Mike Huckabee and Rick Santorum — candidates with close ties to the Christian right — win.

Trump — a New York businessman who can't remember ever asking God for forgiveness for anything — was never a natural fit for these voters. Accordingly, his lead in Iowa has tended to be somewhat smaller than his national lead.

Many evangelical caucus-goers have flirted with supporting Ben Carson, who briefly took the lead from Trump in the state in October. But Carson's support is increasingly looking transient. Recent polls show him down quite a lot from his peak — his 13 percent in both the Monmouth and the Des Moines Register polls are his worst showings in any Iowa poll since August, and confirms a decline that was already evident in the averages.

So now it's Ted Cruz who appears to be the main beneficiary of Carson's collapse. Cruz has cultivated evangelical leaders and groups for years, and notably announced his presidential bid at Liberty University (a hotbed of evangelical activism). He's building a real organization in the state, and appears to be a real threat to win the caucuses — if he can establish a clear lead over the remaining month and a half.

But victories by Cruz, Trump, or Carson would all be horrifying to GOP elites. What about potential establishment savior Marco Rubio?

The news is more mixed for the Florida senator. The Monmouth poll placed Rubio in third, just two points behind Trump. Yet the other two polls place him in fourth, behind Ben Carson, at either 10 or 11 percentage point support. As for Jeb Bush, he sits at fifth place and in the mid single-digits in all three of this week's polls.

This post has been updated with new poll results.