Caucus time is upon us, and on Tuesday more than 100,000 Iowans will trek to their local schools, churches and community centers to kick off the GOP presidential race in earnest, defining the early shape of the campaign and producing 2012's first round of winners and losers.

The latest major poll, taken by the Des Moines Register Dec. 27-30, shows Mitt Romney (24 percent) holding a narrow lead over Ron Paul (22 percent), with Rick Santorum (15 percent) gaining momentum over Newt Gingrich (12 percent), Rick Perry (11 percent) and Michele Bachmann (7 percent).

If one candidate runs away with the Iowa vote, then follows with a landslide in New Hampshire, the Republican primary could be over almost as soon as it started.

Barring that, Republicans could be in for quite a bit of primary campaigning after they pack up and leave the Hawkeye State. After President Obama and Hillary Clinton fought a protracted primary struggle in 2008, the Republican National Committee changed its rules to more closely resemble Democrats' system, doling out delegates to candidates based on proportions of the vote they receive, in the hopes that a longer GOP primary would generate more national interest in the eventual Republican nominee. In 2012, Republican Party officials may get their wish.

In other words: this could take a while.

What's Next

After Iowa, candidates will rush off to New Hampshire to campaign for next week's Granite State primary. Here's a rundown of key upcoming dates:

• New Hampshire primary: Jan. 10. Romney (44 percent) leads handily in New Hampshire, with Ron Paul (17 percent) trailing in a distant second and New Gingrich (16 percent) and Jon Huntsman (9 percent) following, according to the latest major poll there, conducted Dec. 21-27 by CNN/Time/ORC. Huntsman has dedicated the early part of his campaign to the Granite State, and Jan. 10 will reveal whether he can gain legitimate momentum.
• South Carolina primary: Jan. 21. The "First in the South" primary will offer a glimpse at Gingrich's possible staying power. While the former House speaker's polling has dropped in Iowa, an early-December CNN/Time/ORC poll showed him leading by 23 percentage points in South Carolina.
• Florida primary: Jan. 31. The Sunshine State defied Republican Party rules and moved its primary ahead of the Republican National Committee's approved March 6 date in an attempt to preserve its significance, losing half its national delegates as a consequence. Still, only 10 states will send more delegates to Tampa than Florida's 50. Florida is another site of Gingrich's campaign surge, as the former House speaker took in a whopping 48 percent to Romney's 25 percent in an early-December CNN/Time/ORC poll.
• Nevada caucuses: Feb. 4. The first Western state to pick a candidate, Nevada has seen Romney emerge with a narrow lead, but polling has been scarce.
• Super Tuesday: March 6. If a clear leader hasn't emerged by March 6, Super Tuesday could bring some clarity. Voting will occur in 11 states - Alaska, Idaho, Georgia, Massachusetts, North Dakota, Ohio, Vermont, Virginia, Tennessee, and Texas-to award a total of 497 delegates out of 2282 total. By that time, 28 percent of all delegates will have been awarded
• California primary: June 5. In the unlikely event that Republicans are still campaigning against each other, Californians will cast their potentially decisive votes second to last; Utah will end the primary season with its June 26 contest. California will award more national delegates than any other state.

How Long Will It Take?

As past elections have taught us, a candidate could wrap up the nomination with a few decisive wins in early states - and Romney appears poised to finish well in both Iowa and New Hampshire.

But the contest could drag on. If no clear frontrunner emerges after the first few contest, the GOP primary could become a race for delegates, and the Republican party's new rules, adopted in August, could turn the early-state skirmishes into a long, national war.

To win the Republican nomination, a candidate will need the support of a majority (1144) of all national delegates (2286 total). Should the current poll leader Romney emerge as the winner of several early states, another candidate could keep campaigning to unite a bloc of delegates against him. Paul, as BuzzFeed's Ben Smith has reported, is laying the groundwork for such a race - following the Obama campaign's playbook of organizing for delegates in states that were all but ignored by other campaigns.

The Republican Party will use a byzantine system of delegate allocation in 2012, after its rule change was designed to mimic the drawn-out Obama/Clinton battle that drew national interest. Almost every state will use a different system of assigning its delegates to presidential candidates, and some will use county, congressional-district, and state conventions to pick delegates to the August convention in Tampa, Fla. The new process will give far more opportunities to organize for delegates down the road.

A Delegate Race?

If the race isn't decided soon, attention will turn from national and state polls to delegate counts, just as it did for Obama and Clinton in 2008. And nearly half of all Republican delegates will be awarded in April or later.

By the end of January's contests, only five percent of all GOP delegates will have been won. On the eve of Super Tuesday, only eight percent will have been awarded, and when Super Tuesday is over, 28 percent will have been awarded. A leading candidate could campaign into April, winning every single delegate available, and still not have the nomination mathematically clinched.

If that happens, campaign organizations could be put to the test, and the GOP 2012 contest could look a lot like the Democrats' race in 2008.

Elizabeth Hartfield contributed to this report.