Story highlights David Gergen: Republicans have a strong chance of taking the White House

He says the Iowa results don't help their cause, since there's no clear winner

He says Romney is still the likeliest nominee, but Santorum or Gingrich could win

Gergen says there's even still a chance for a new candidate to enter the race

Republicans this year have the best chance of defeating a sitting Democratic president since Ronald Reagan toppled Jimmy Carter more than three decades ago, but Democratic heavyweights are quietly celebrating the fact that, given Tuesday night's caucus results, that task has just become harder.

For Democrats, the rising fear was that Mitt Romney would storm to victory in Iowa and New Hampshire, not only ending the GOP nomination fight but quickly uniting his party behind a candidate who has consistently shown the greatest potential against President Barack Obama. Romney would have gained the muscularity and glow of a star.

While he did win the caucuses last night and should still sweep New Hampshire, the manner of his victory in Iowa hardly sent a message of strength and unity.

Consider: The percentage of votes that he won was virtually the same as four years ago when he lost Iowa to Mike Huckabee and the actual number of votes was six less. That's not much progress for a candidate who has been courting Iowans off and on for five years. Moreover, his percentage of votes is the lowest any winner has recorded in the 40-year history of the Iowa caucuses. Republicans did have a respectable turnout of some 122,000 -- modestly better than four years ago -- but it was not the burst of excitement they had hoped. This is a party that hasn't yet found its leader.

Where do Republicans go from here in their search for a nominee? There appear to be three possible scenarios:

David Gergen

(1) The probability: Romney marches on to victory in Tampa (my guess: 65% likelihood). He retains the best ground game among Republicans -- both money and organization -- and with so many opponents still in the field, he can play the divide-and-conquer strategy that helped him eke out a victory in Iowa.

Rick Perry's odd decision to stay in the race was a boon for Romney, whose best path forward is to roll up a double-digit victory in New Hampshire and then, boosted by South Carolina Gov. Nikki Haley (who recently endorsed him), pull off an upset in the Palmetto State 11 days later. He would then be poised to win in Florida -- and if that happened, he could achieve what he had hoped early on: to shut down the race. Even if he were to lose South Carolina, he is still in the best position to grind out victories over the long haul.

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It is worth remembering that while they had reservations about him, many Iowans voted for Romney because they thought he had the best chance to win and also to turn around the economy. He still has those assets.

Results from a December Gallup poll are also important to Romney's argument: That poll asked voters to place themselves on an ideological scale of 0-5, running from strong liberal to strong conservative. Strikingly, the average for the public at large was 3.2, to the right of center (2.5). Just as strikingly, voters put Obama at 2.3 and Romney at 3.5. In short, voters saw Romney as being much closer to their point of view than the current president.

(2) The possibility: A more conservative candidate takes it away from Romney (25% likelihood). Conservative activists clearly don't want Romney and their distaste may be growing. But it will be hard for them to beat him unless they can coalesce behind a single candidate. The man with the best chance of that now is Rick Santorum. He has a chance to capture the media spotlight now and, as he showed in his moving speech after the Iowa caucuses, he has the capacity to connect with voters emotionally as well.

The early signs for him in New Hampshire are encouraging, but by no means overwhelming: Wednesday's CNN/ORC poll of likely primary voters in New Hampshire who watched the Iowa caucus coverage saw Santorum's support double from 5% to 10%, drawing mostly from Gingrich, who declined from 12% to 9%. But Romney stayed level at 47% -- and unless Santorum can significantly cut Romney's lead in New Hampshire or pull off another stunning come-from-behind victory in South Carolina (where Santorum is still in the low single digits), it's hard to see him taking a commanding hold of the alternative-to-Romney mantle.

Another possibility is Gingrich, who, though hobbled by last night's underwhelming result, still could vault himself back into contention with a dominant march through the South. Polling in South Carolina and Florida has been sparse since the holidays, but as of mid-December he still clung to solid leads in both of those states. That was before his rivals (as well as several of his former colleagues) had fully sharpened their knives for him -- and the Gingrich who spoke last night seemed ready to return the favor with a crusade against Romney. Still, if he can channel those frustrations into boffo performances in South Carolina and Florida, he will spring back into contention.

There is likewise the distant possibility that former ambassador to China and Utah governor Jon Huntsman could be the latest candidate to catch fire and could hold the enthusiasm long enough to build a consensus around his candidacy within the party.

The conservative establishment would be willing to adopt him if he were viable -- the Washington Post's George Will and the Wall Street Journal's editorial board have both been charmed by his conservative policy credentials -- but his campaign messaging has seemed almost completely to ignore the more conservative wing of the party and his debate performances have been uninspiring.

If he was counting on a rush of exposure in the week leading up to New Hampshire, he likely just forfeited a lot of that attention to the Santorum buzz. Ditto for libertarian hero and Texas Rep. Ron Paul, who probably hit his high-water mark in Iowa and will likely see his still-impressive third-place finish eclipsed by the Santorum coverage. All of which leaves us with one other potential alternative:

(3) The long shot: Someone else enters the campaign (10% chance or less). Normally, this late in the game, a new entrant to the contest would be the stuff of science fiction. But conservative voters seem to be singularly dismayed by the choices in front of them: as CNN's Erick Erickson tweeted last night, "Typical of email I'm getting: 'If you put a gun to my head and said Romney or Santorum I would say pull the trigger.'"

Who would step into the fray? One hears voters pining for New Jersey Gov. Chris Christie (unlikely to join, especially after endorsing Romney) and some have floated Louisiana Gov. Bobby Jindal (who endorsed Perry). Former Florida Gov. Jeb Bush would be a strong candidate, but that may be a tough sell to Bushed-out voters only four years after the conclusion of his brother's presidency.

Would a candidate who jumped in this late even have a path to victory? Perhaps. The early primaries and caucuses are richer in symbolic significance than they are in delegates, especially with the new rules prohibiting winner-take-all allotment of delegates in the early states. And even with such a late jump on fundraising and organization-building, a candidate who was able to rack up a string of impressive victories in the middle- and later-term primaries could theoretically build up a big enough head of steam to take the convention by storm while making use of the Internet and earned (read: free) media coverage to play catch-up on money and organization.

The late-entrant scenario is still a dark horse at best, but even the fact that it's within the realm of possibility underscores the reason Democrats are quietly cheering last night's outcome: the GOP is still, at best, a party that's looking for a standard-bearer -- or, more dangerously for their 2012 prospects, a disunited collection of smaller groups of voters still pushing their own.