If you’ve waken up (or are still up) from a long night of caucus-watching, you’re probably wondering what led Iowa voters to split almost evenly between Mitt Romney and Rick Santorum, with Ron Paul close behind. Here’s our take based on final entrance poll results among Iowa caucus-goers.

The three candidates at the top of the Iowa Republican caucus results have distinct constituencies, ones that echo broader divisions within the GOP.

Romney’s single best group in a caucus-night poll of voters consisted of those who prioritize beating President Obama over other candidate qualities. He won nearly half of all such voters, more than double the number selecting any other candidate. Romney also fared relatively well among moderates and liberals, even as he slipped among the most conservative caucus-goers compared with his performance four years ago in the state. The former Massachusetts governor also topped his competitors among those saying the economy was their top voting issue.

(In case you missed it, check out how Romney and Paul performed compared to 2008)

“Very conservative” caucus-goers broke for Santorum, according to the poll. The former senator is the newest darling of the tea party political movement, picking up 30 percent of strong tea party backers, with four other candidates in the teens. Santorum does best among those voters prioritizing abortion as an issue and “strong moral character” as a candidate attribute. The senator surged in the closing days of the campaign, and won a plurality of those saying they made their final decision Tuesday.

Paul is buoyed by strong support among younger voters and independents, with both groups making up a larger share of caucus-goers than they did four years ago. Paul picked up nearly half of caucus-goers under 30 years old and more than four in 10 independents. The Texas congressman also battled Santorum among voters singling out being “a true conservative” as a top quality.

Evangelical Christians - who delivered Mike Huckabee a resounding victory in 2008 - were less united this year, with no candidate garnering more than a third of the evangelical vote. Santorum came closest, with 32 percent support in preliminary entrance poll numbers. Paul earns 18 percent, with Romney, Newt Gingrich and Rick Perry all at 14 percent. (Read more about the 2012 evangelical vote here.)

Other highlights:

Santorum’s vote concentrated among social conservatives Fully 79 percent of Santorum’s supporters were evangelical Christians and 31 percent of Santorum’s supporters chose abortion as the most important issue facing the country, while 34 percent chose the economy. Among all caucus-goers, 57 percent identified as evangelicals and a slender 13 percent said abortion was the top issue.

Where’s Bachmann’s base? Rep. Michele Bachmann - who won the Ames straw poll in August and is the first candidate to drop out of the race since voting began - failed to clear double-digits in any group in the Iowa caucus entrance poll. She pulled just 9 percent among strong tea party supporters, a group that fueled her rise this past summer.

Late deciders - About one in five caucus-goers (18 percent) made their decision on Tuesday; almost half decided within the past week. Confirming his late surge in polls, Santorum won more than a third of late deciders. Paul won nearly four in 10 voters who decided before December; over a quarter of this group eventually chose Romney.

Strong turnout - Edison Media Research estimates 123,000 voters participated in the Republican caucuses, topping the record of 119,000 set four years ago. Still, the new figure is only about half the number showing up on the Democratic side in 2008.

What if Perry drops? After a fifth-place finish, Texas governor Rick Perry said he would return to Texas to reassess his candidacy. In the entrance poll, Perry’s best groups were also among Santorum’s best and Romney’s worst -- those prioritizing character, evangelicals and tea party backers.

These are final results from the Republican caucus poll of 1,737 voters as they entered 40 randomly selected caucus voting places in Iowa on Jan. 3, 2012. The poll was conducted by Edison Media Research for National Election Pool, The Washington Post and other media organizations. The results for typical characteristics have a margin of sampling error of plus or minus four percentage points.

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