On Saturday night, the Des Moines Register released its final major poll of the Republican presidential field before voters weigh in at Tuesday's Iowa caucuses. The Register's "much-respected" Iowa Poll has a strong track record: In 2008, it correctly predicted caucus victories for Barack Obama and Mike Huckabee. This time around, the poll shows a three-way race between Mitt Romney (24 percent), Ron Paul (22 percent), and Rick Santorum (15 percent) — a result that would have shocked observers even a few weeks ago. What does this poll tell us about the GOP race? Here, five takeaways:

1. A still-surging Santorum could win
Rick Santorum jumped from 6 percent in the Register's November poll to 15 percent in the new one, putting him solidly in the top tier. "But get this about Santorum's surge," say Chuck Todd, Mark Murray, and Domenico Montanaro at MSNBC: In the final two days of the poll's four-day sample, Santorum came in a strong second, running neck-and-neck with Romney. "Bottom line: You can see how Santorum might be able to win this thing, especially if Perry and Gingrich supporters" defect. And they're more likely to jump to Santorum as he looks increasingly like the winning non-Romney, says Alexander Burns at Politico. Remember, "a late, authoritative survey like this one can also end up being a self-fulfilling prophecy."

2. Romney was smart to go all-in in Iowa
The former Massachusetts governor is still publicly downplaying his chances in Iowa, says Christopher Rowland in The Boston Globe, but his lead in the Register poll fueled "a clear sense of momentum" in the Romney camp. "If Romney wins Iowa and then New Hampshire, that might be enough even for South Carolinians to consider the virtues of wrapping up the nomination fight early," says Ed Morrissey at Hot Air. And since a Santorum or Paul victory is less threatening to Romney than a win by Gingrich or Perry, Romney will benefit even if he comes in second place in Iowa.

3. It's looking grim for Perry
The Iowa Poll clearly divides the GOP field into two tiers, says Steve Benen at Washington Monthly. And the second-stringers — Newt Gingrich, Rick Perry, and Michele Bachmann — can only "hope Iowa doesn't derail their entire campaign." No candidate has more to lose than Perry, says Nate Silver at The New York Times. Despite his "formidable résumé," intense focus on Iowa, and multi-million-dollar advertising budget, the poll shows him treading water in the second tier. That's why Perry is aiming his fire at Santorum, says E.J. Dionne at The Washington Post. They're fighting for the same evangelical voters, so "a surging Santorum will start gobbling up Perry's vote."

4. But it's still a wide-open race
This contest is still very competitive, says Washington Monthly's Benen. "More than 40 percent of likely caucusgoers say they could still be persuaded to change their minds,'" and even "apparent frontrunner" Romney's lead "comes with caveats." At 24 percent, he's "effectively at the same level as he was in October." Yes, "the results on Tuesday night could look dramatically different from any poll today," says Fox News. "There are going to be three tickets out of Iowa," Tim Albrecht, spokesman for Gov. Terry Branstad (R), tells Fox. "I think a case can be made for all six to get one of those three tickets."

5. The surges are getting much shorter
"If Santorum wins this, he will have had a surge of a week, or less," says David Weigel at Slate. And if Paul loses, it may be because his surge only lasted 10 days, ending Dec. 28, according to the Register's polling. That's about par for the course for this boom-and-bust GOP primary. In July and August, Bachmann's surge lasted 44 days. Then Perry was on top for 32 days. Herman Cain led the field for 33, and the much-ballyhooed Gingrich surge lasted only 27 days. Santorum may have surged at just the right time. We'll find out Tuesday.