Ed touched on this in his post about the new Fox News poll of Iowa but I thought people would want to see what the trend lines look like. Here’s RCP’s average of various polls of Iowa since New Year’s. The blue line is Trump, the black line is Cruz.

“Fair enough,” you say, “but some of those polls are unreliable. Shouldn’t we rate the numbers from more reliable pollsters more heavily?” Well, FiveThirtyEight did that. Here’s what the state of the race looks like to them:

They still have Cruz as a favorite to win when you factor in everything — state polls, endorsements, and other intangibles — but follow the link and you’ll see that Trump is moving up in that measurement too. As recently as a week ago, Cruz’s odds of winning Iowa were north of 50 percent while Trump’s odds were a little higher than 25 percent. Now? Cruz 48, Trump 41. Every poll-watcher in America is waiting for this weekend’s Selzer poll of Iowa for the Des Moines Register, which had Cruz ahead of Trump by 10 points in mid-December but just three points in mid-January, further evidence of movement towards Trump. If Selzer has Trump ahead, you’ll see white-knuckle panic among anti-Trumpers on Monday morning as Iowans get ready for the big night.

If you look back at the RCP graph above, you can see it’s divided into roughly three periods: Cruz’s lead suddenly falls off, Cruz and Trump are roughly even in the polls, and then Trump starts to pull away. Some of that may simply be late-deciders making up their minds, although traditionally most of the late-deciding will happen this week, within seven days of the caucus. Maybe what we’re seeing in these numbers is the start of a late break towards Trump. If you’re looking for silver-bullet explanations, though, you could spitball something like the following. Trump starts talking about Cruz’s “natural-born” eligibility around January 4th; most voters don’t care, but a small but significant part of Cruz’s base is troubled by it and shifts back to undecided. Trump and Cruz then clash at the debate on January 14th producing several days of stasis, with Trump inching the tiniest bit ahead. Then, on the 19th, Cruz gets hit with a double whammy — Palin endorses Trump and Terry Branstad warns Iowans that it’s the end of the ethanol gravy train if Cruz becomes president. On the 19th, Trump leads Cruz by 1.1 points; a few days later, he leads by 2.7. Just within the past 72 hours, his lead has jumped again, although whether that’s residual momentum from all of the things I’ve just described or new support based on, say, his claims that Cruz is a Goldman Sachs cronyist or the fact that various congressional Republicans are signaling they prefer him to Cruz is impossible to say.

If you’re a Cruz fan, the response to all this can be summarized in 10 points. Point one: Turnout. Point two: Turnout. Points three through 10: Turnout. Cruz supporter Steve Deace argues that to believe Trump will overwhelm Cruz, you need to believe turnout on Monday night will be vastly larger than it’s ever been for a caucus, even though Cruz’s organization there is superior to Trump’s.

So now we have FOX as well as CNN producing polls this week that show 300,000 Iowans are voting in the Iowa Caucuses, and therefore Trump with a double-digit lead. Allow me to put those projected turnout numbers in perspective:

–That’s about a 200% voter increase from the highest Iowa Caucus turnout ever back in 2008.
–The most voters we’ve had in a primary (which always has higher turnout) in Iowa this century is only 230,000. And our last U.S. Senate primary had only roughly 150,000 voters in 2014.
–There are actually 11,000 fewer registered Republicans in Iowa this January than in January 2015.

Not only that, notes Deace, but Iowa polls — with Selzer a notable exception — have famously missed the true state of the race on the eve of the caucuses before, with Rick Santorum an also-ran in RCP’s final polling average before he shocked everyone with a win in Iowa in 2012. Erick Erickson thinks the caucus format works against Trump too:

The problem with polling Iowa is that a caucus is not a primary. With a primary, voters go to a polling booth, click the name of the candidate who they support, and leave. With a caucus, often not even in the same location as where voters go to vote in primaries, there is an hour commitment, the voter must be in the room by seven o’clock in the evening, and they must show their support rather publicly.

People who show up for primaries may not know the caucus location, they may not realize they have to stay an hour, and they may think they can show up late. Likewise, we know historic turnout models for caucuses and many of the late polls with a huge Trump lead have turnout models that far exceed even the most historic high turnouts of caucuses past.

That said, Erickson thinks Trump is ahead narrowly. That’s the safe bet right now — it’s hard to believe, even with a dubious recent history, that this many pollsters would be wrong, especially when Trump’s unique potential to turn out huge numbers is well-known. Obamamania ensured that 57 percent(!) of caucusgoers in 2008 were first-timers, but O had a superb organization and had spent many months campaigning on the ground in Iowa. Neither of those things is true of Trump. On the other hand, even the Obama phenomenon circa 2008 didn’t have Trump’s celebrity reach. If Trump spends the next week broadcasting the fact that independents are free to register with a party on caucus night and participate, thousands of independents could show up, sign up as Republicans, and completely blow up the turnout models. Right now pollsters are estimating that something like 30 percent of caucusgoers will be first-timers; Adrian Grey thinks it’ll be closer to 40 percent, which likely means more Trump voters than everyone expects. The current polls may be right, and possibly are even underestimating Trump’s lead.

Just as I’m writing this, ARG is out with a new poll of Iowa. Last week, Trump led Cruz by four points, 29/25. Now: Trump 33, Cruz 26. That’s right in line with all of the other recent polls showing Trump edging above 30 percent and expanding his lead over Cruz. A lot of people will have been wrong if Cruz ends up pulling this out.