Barring an unforeseen development, Mitt Romney will come in first or second in the Iowa caucuses tonight and win the New Hampshire primary handily. The question then becomes whether he can be beaten, and if so, who can do it.

It’s easy to argue that about 70 percent of the Iowa caucus-goers will vote for someone else tonight. But, of course, more than 70 percent will likely vote against the others. It is not enough to point out that in a multi-candidate field Romney is below 50 percent. The only way, I would suggest< that he can be dislodged is for the race to very quickly come down to a one-on-one race with a viable, well-financed opponent.

This is where we started a year ago, right? Then, there was the prospect of Indiana Gov. Mitch Daniels, Rep. Mike Pence (R-Ind.), New Jersey Gov. Chris Christie and a batch of other candidates joining the race. But none emerged. And of those who have competed each has melted in the spotlight after attaining the lead position as the not-Romney candidate. There appears to be no desire among Republican voters to reconsider the already discarded candidates. Newt Gingrich, Texas Gov. Rick Perry and Rep. Michele Bachmann (R-Minn.) haven’t managed to revive themselves. Absent a miraculous finish in the top three by one of them tonight, it’s hard to conceive that any of them will be able to collect the money and support needed to win in states far less suited to them than Iowa (e.g. Nevada, Florida, Michigan).

That leaves Rick Santorum and Rep. Ron Paul (R-Tex.). Santorum, the pundits argue, has too many Senate votes to which die-hard conservatives will object. He voted for some earmarks and supported No Child Left Behind. Really, that’s the Achilles’ heel? Frankly, that’s the worst argument against Santorum. His social and foreign policy bona fides are the equal of anyone in the race, and his promises on tax reduction and spending restraint are likely more than sufficient to pass muster with the base. He’s certainly to the right of Gingrich in his voting record and opposed both the individual mandate and TARP (which Romney supported).

His real dilemma is that rest of the field, which seems intent on hanging around. Perry, now running ads bashing Santorum, promises to stick around for South Carolina and may have at least PAC money to sustain his effort. Bachmann, Gingrich and Paul insist they are continuing on as well. Precisely as the field did in 2008, the candidates on the right will be vying for the same Christian conservative vote in South Carolina, while Romney (likely without even a murmur from Jon Huntsman, who will come and go in New Hampshire) will have the rest of the electorate to himself. This is how Sen. John McCain (R-Ariz.) beat Mike Huckabee, Fred Thompson and Romney in 2008.

If Santorum could clear the field he’d have a shot in a state ideally suited to some economic populism and rock-solid social conservatism. It becomes monumentally more difficult, considering Romney’s money advantage and the momentum coming out of the first two primaries, for him to win outright in South Carolina with everyone else still in the race. And if he should eke out a win, there looms Florida, an extraordinarily expensive state that is more ideologically diverse than the three states preceding it.

Will the anti-Romney voices begin beating the drum for other candidates to get out and clear the way for Santorum? Perhaps. But even if they did it is far from clear any of the contenders would listen. The race has been too volatile for candidates to give up this early. Hope springs eternal that Santorum will fade and they’ll get their second chance.

Then there is Paul, whose brand of conspiratorial libertarianism has taken a hit in Iowa. His strength has been in small groups, where the fervor of his followers can out-shout and out-vote competitors’ most devoted forces. But consider this: Iowa will have 130,000 or so caucus-goers; South Carolina will have more than 400,000 primary voters. And Florida’s primary turnout is likely to be about 2 million. Does anyone think Paul has enough supporters to win races of that size?

Well, what about the “late entrant”? That seems more and more like a pipe dream with each passing day. If Romney comes out of New Hampshire with a head of steam, which conservative alternative (who already turned down a chance to run) would risk challenging him? And if someone did emerge, the vote would be even further divided among not-Romney candidates.

Frankly, the only one who can beat Romney, if other not-Romney contenders don’t clear the field for Santorum, is Romney. A significant gaffe or a rotten debate performance may open a crack in his fortress. Others have tried to rattle him him with little success, and he seems to be more comfortable in TV interviews. The chances, therefore, are not great that this will occur. Unless Romney takes his victory for granted or makes a game-changing error, it’s hard to figure out how he is dislodged. (No wonder he’s adopted the “earn it” slogan in New Hampshire.)

In sum, if the right can’t unite around the most viable alternative to Romney, who will likely be Santorum, it will be — despite all the talk of how much the Tea Party has changed the GOP and how different politics has become in the Twitter world — another GOP primary race in which the runner-up last time wins it this time around.

Perhaps the base should have been kinder to Jon Huntsman. The best-kept secret of the 2008 race is that had Rudy Giuliani not collapsed and instead competed ably with McCain for the moderate GOP vote, Romney would have won the nomination. This time Huntsman is the Rudy candidate — the too-weak moderate who gives the non-hard-core conservative a clear path to the nomination.