Then there were six.

After the closest caucuses in Iowa history -- just eight votes separated Mitt Romney and Rick Santorum Tuesday -- the Republican field has been whittled down to the two of them plus Newt Gingrich, Jon Huntsman, Ron Paul and Rick Perry.

Michele Bachmann, who finished sixth in Iowa with just 5 percent of the vote, announced Wednesday morning that she would suspend her presidential campaign, despite previous vows to compete at least through the South Carolina primary on Jan. 21.

Gingrich and Perry have chosen to continue at least through South Carolina and potentially Florida, but if they don't score big wins there, they, too, will be out of the race -- if not officially, then functionally. Huntsman, meanwhile, has staked everything on a strong showing in New Hampshire, and his campaign will be over as well if he does not exceed expectations next Tuesday.

In other words, Iowa voters did what they do best: They narrowed the field by separating the viable candidates from the wannabes and has-beens. Their choices bring the big picture into sharper relief -- and it's not just about the numbers.

Mitt Romney

Romney, who squeaked out an eight-vote victory in a state he had barely campaigned in before the final weeks, gains momentum from performing so well in spite of his minimal on-the-ground efforts and socially conservative voters' well-publicized distrust of him.

We should not underestimate the significance of Romney's victory, despite the fact that it was by a razor-thin margin, Costas Panagopoulos, a political scientist at Fordham University in New York, told the International Business Times. What's important is just how far Romney came in this process to manage to clinch this victory from a campaign that had largely overlooked Iowa, almost discounted it entirely.

It would be a mistake to say that Iowa clinched the nomination for Romney, even presuming he wins as big in New Hampshire as polls would indicate. For one thing, after New Hampshire, he will have to head to South Carolina and once again prove that he can compete on conservative turf -- and if Gingrich has a strong showing there, he may re-emerge as a viable challenger to Romney despite his fourth-place finish in Iowa.

But while the race is far from over, Romney is in about as good a position as he could hope for.

Unless there is some dramatic surprise, such as something on the order of the damaging stories that came out about President Clinton right before the 1992 New Hampshire primary, the likelihood that one of the other candidates will get the nomination is slim, Jamie Chandler, a political scientist at Hunter College in New York, told IBTimes.

Rick Santorum

Santorum, meanwhile, gains momentum from the fact that, until a couple weeks ago, he was expected to finish dead last in the caucuses. To pull a virtual tie for first place out of that sort of wreckage is a remarkable feat, and it is giving Santorum a burst of who is this guy? attention.

Whether he can sustain that attention and build a national support base when his campaign never really expected to move beyond Iowa is another question. It's not impossible, Panagopoulos said, but it is unlikely.

Can he build on that momentum and really develop the kind of infrastructure and get the kind of financial support that's necessary to be competitive in the subsequent contests? Panagopoulos asked. It would have been helpful to Santorum if Rick Perry had decided to step aside, but with Perry still in the race at least through South Carolina, the social conservative voters are likely to continue to be split.

He and Chandler both noted that Santorum has so far escaped the intense media scrutiny that brought down so many Iowa hopefuls before him, simply because he surged so late -- but he will face it in full force now.

The press coverage will mute any momentum Santorum got out of Iowa, Chandler said. Because of the scrutiny he'll be under, there will be a lot more discussion about his far-right, offensive past statements about his support of categorical annulments of gay marriage, forced divorce, income inequality, as well as his recent statement that President Obama should oppose abortion because he is black, his opposition to food stamps, and women's rights.

As has been the case with many conservative candidates who rose briefly to challenge Romney, he will have to defend his ability to be competitive not only in subsequent primaries and caucuses but also in the general election, Panagopoulos said. I think Santorum has his work cut out for him to do that successfully.

Ron Paul

Paul's performance in Iowa is a bit tougher to interpret.

From one perspective, third place -- and a very close third place, at that -- is a major validation for a campaign that has faced dismissal or mockery for most of its existence. From another, losing to a last-minute upstart like Santorum is somewhat embarrassing for a campaign that, in the couple weeks leading up to the primary, had really expected to place first or second.

There is also the practical consideration: Paul needed to come out of Iowa with enough momentum to carry him through New Hampshire and into South Carolina, where he is polling much lower. That he took momentum from his finish in Iowa is indisputable, but will it be enough to earn him a strong second-place finish in New Hampshire (catching Romney, who leads by 20 points, is unlikely with so little time remaining), which would in turn give him a fighting chance in South Carolina and Florida?

It's important not to discount his performance in the Iowa caucuses, but the results do suggest there are limits -- voters will not completely overlook questions of electability, Panagopoulos said. Even those voters who wanted to make a statement by supporting Ron Paul, at the end of the day had to decide whether that was worth taking a vote away from someone who could potentially go on to be competitive in the general election.

Whether Paul could be competitive in the general election is a topic of much dispute.

His support among the overall electorate may be stronger than it is among Republican primary voters, because a large portion of his support in the Iowa caucuses came from independent voters and even Democrats, many of whom are attracted to his views on foreign policy and civil liberties. His supporters would argue that this makes him a strong candidate to take on Barack Obama in November -- perhaps stronger than the more mainstream GOP candidates, who would have a harder time picking off non-Republican support.

Polls, for what they are worth, show a somewhat different picture. In head-to-head matchups from December, Obama leads Paul by an average margin of 7.7 percentage points. Paul does better against Obama than Gingrich, Huntsman, Perry or Santorum, but Romney does the best. Obama leads him by an average margin of 2.2 percentage points, and three polls show Romney either tying or beating Obama.

No poll has shown Paul less than 5 points behind Obama -- but of course, that could change quickly if he managed to win the nomination and spread his message on a national scale.

Chandler and Panagopoulos agreed that Paul would have a substantial impact on the race in terms of influencing the eventual nominee, but they thought he was unlikely to be the nominee himself.

I think it will be tough to argue that there's really a strong possibility of a Ron Paul nomination, Panagopoulos said, but I think he's doing well enough to warrant a stage on the national Republican scene for quite some time to come.

Winning Isn't Everything

It is important to note that, with the Republican Party as divided as it is, candidates who do well in the primaries but don't win the nomination will still have a chance to influence the nominee going into the general election.

Santorum said on Meet the Press last Sunday that there were three different races happening: the establishment race, between Romney and Gingrich; the libertarian race, cornered by Paul; and the conservative race, between him, Perry and (no longer) Bachmann. This is true. The ideological divisions are remarkable in their starkness, and they will have a profound effect on the general election no matter who gets the nomination.

The eventual nominee is going to have to do some heavy work uniting the party, most likely through his vice president choice, Chandler said. Perry or Bachmann, for example, would help Romney balance the ticket, since the Midwest and the evangelical vote is going to be an important determinant of whether or not he wins in November.

By the same token, just as Romney will have to make some concessions to evangelicals if he is the nominee, he will also have to make some concessions to libertarians, who account for a growing share of the electorate.

That's where Ron Paul comes in.

It will be interesting to see whether, if Paul does not win the nomination, he will consider or be considered for the running-mate slot. But even if that doesn't happen, the depth of support for his ideology will leach into the nominee's platform to some extent.

Ron Paul's performance in Iowa is significant because it demonstrates a growing tide of support for libertarianism, especially among young voters, Chandler said. His role this season is to be a catalyst for change and raise the profile of libertarianism. Over the next several years, it's likely that we'll see an evolved version of Paul's philosophy become the dominant Republican ideology.

Nomination or no nomination, influencing the Republican Party to that degree would be a huge accomplishment for Paul.