The indispensable Mark Blumenthal of has so many great nuggets in his Iowa wrap-up that you really should read it yourself. But, herewith, some highlights for those short on time:

1.) The Huckabee-Romney race could be close, or it could be lop-sided. It really depends on the turnout of rural voters and evangelicals relative to "mainline" Republicans, which pollsters are notoriously bad at predicting. But, says Mark, "it is worth remembering that one of the biggest misses in pre-Caucus polling was back in 1988 when Pat Roberston finished second (ahead of George H.W. Bush) with 25% of the caucus vote. Polls had shown Robertson running a distant third, receiving 17% in one poll, single digits in most others."

2.) On the question of second-choice preferences, keep in mind that most of them won't matter. After all, Edwards, Obama, and Clinton are going to be viable in almost all their precincts, so their supporters will rarely reallocate. It's the second-choice preferences of Biden, Richardson, Dodd, and Kucinich supporters that we want to know about. According to Mark, this calculus slightly favors Edwards, but it's somewhat ambiguous:

Four recent polls have done the reallocation of Richardson, Biden, Dodd and Kucinich supporters statewide, and guess what? Once again, the Des Moines Register poll tells a different story. The other three all show the reallocation working in Edwards's favor -- and by a net six and eight points by respectively, Mason-Dixon and InsiderAdvantage. Zogby's first numbers from Sunday show small single digit benefit to Edwards and their report today implies the same. The Register reports, however, "that the results would change little if the votes for the lower-rated candidates were redistributed among the front-runners." So here is yet another unresolved conflict that only the actual results will resolve.

3.) Wondering why Obama took a dip and Hillary seemed to surge in polls conducted last week, while the dynamic has reversed in more recent polls? Mark's theory, sketched out by one of his commenters, is that Obama supporters are more likely to travel over the holidays because of their relative affluence. As Mark's commenter puts it:

Before I left for vacation, Obama was trending up at 29%. A few days after I got home from vacation, Obama's sensitive trend estimate shows him gaining ground and actually now at 30%, right in line with pre-vacation trends.

Only, in between, his numbers plummeted. ...

The sensitive estimate, basically, is right in line with where the race was at 10 days-2 weeks ago. But everything in between has been the complete reverse of that period.

The period where everything flipped on its head was, of course, a time when most everyone who can go on vacation does go on vacation. And the DMR poll's cross-tabs certainly suggest that among the block of voters I'd guess are more likely to leave home over the winter holiday, Obama cleans up: ~40% to 20% each for Hillary and Edwards amongst college educated and those making over 60K. Meanwhile, the less-educated and less-affluent constituencies that support Clinton and to a lesser extent Edwards strike me as precisely the type of voter who will be home more often over the winter holiday.

I'd add another wrinkle to this story: Obama is famously courting out-of-state students who attend college in Iowa. (The caucus rules allow them to participate.) Those strike me as the kind of people who would have gone home (i.e., out of state) for vacation, then returned a couple days before the caucus so they could turn out for Obama. Moreover, it wouldn't surprise me if a lot of them returned to Iowa on December 30 or 31. That was a natural vacation-ending point--Sunday or Monday--and, if memory serves, it's a lot more fun to hang out with other students on New Year's Eve than with your family. (No offense to any family member who might be reading this...)

Of course, this may be a relatively small group of people, so it's unclear how much it would have affected the polling results. But I could see it making a difference at the margins, which is of course what we're talking about.

4.) Mark makes a great point about post-caucus spin--somewhat similar to the one Isaac made yesterday. In a nutshell, he says it's risky for Mark Penn and Harrison Hickman (the Clinton and Edwards pollsters, respectively) to dismiss Obama's lead in the Des Moines Register poll as the product of an "unprecedented" number of independents and first-time caucusgoers:

[B]y elevating a bit of polling wonkery--the argument over independents--into a two-day front page story, Obama's opponents have helped hand him more than a 'momentum' story on the eve of the caucuses. His precinct captains now also have a strong electability argument to make tomorrow night: Obama attracts independents.

But more important, what if the Register is right? What if an influx of first-time caucus goers propels Obama to a modest victory margin? Given their spin yesterday, it will be quite a challenge for the other campaigns to shrug it off as an inconsequential result they saw coming all along. Now, if Obama wins with the help of a wave of caucus newcomers, it's not just a "win," it's an "unprecedented departure," a result "at odds with history," perhaps even a "revolution." [All of these are quotes rival pollsters had used to deride the Register poll.]

Indeed. It could be painful to watch the Clinton and Edwards campaigns walk those words back in the event of a clear Obama victory.

--Noam Scheiber