Ron Paul? He may well win Iowa – and even New Hampshire, which admittedly would throw Mr. Romney for a bit of a loop – but his base of support just isn't broad enough to get the actual nomination, especially once success causes the other candidates to turn their negativity on him.
Rick Perry? Jon Huntsman? If the field is blown wide open by early Paul wins, combined with a dismal showing by Romney, then it's possible one of them could become a factor – this is, after all, one of the most volatile primary contests in recent memory, and fortunes can shift quickly. But given where they both are right now, it seems a monumental task.
Rick Santorum and Michele Bachmann barely seem worth mentioning at this point.
Which leaves... Romney. It may be one reason that more and more key GOP figures are coalescing around him.
Romney has always been more the choice of the Republican establishment, but now he's starting to win endorsements from key conservatives outside the establishment as well.
South Carolina Gov. Nikki Haley (one of Sarah Palin's "Mama Grizzlies") is one of the most high-profile recent examples. And he has the endorsement of Christine O'Donnell – the tea party favorite who won the Delaware primary (and lost the general election) despite having the GOP establishment against her.
Certainly, some of the most important GOP figures are still waiting to give their blessing. The Washington Post's endorsement tracker shows just 9 of the 50 Republican VIPs it's watching, six of whom have endorsed Romney.
And endorsements – particularly taken individually – only carry so much weight. But if they continue to pile up in Romney's favor, they could start to give a collective boost to a candidate notable for his consistency but who has still struggled to generate enthusiasm among a big swath of the electorate.
"Elected officials rarely 'deliver' votes in the manner of the party bosses who once controlled large blocks of convention delegates," notes a HuffPost analysis. "But political scientists have demonstrated that endorsements by party leaders and activists are an important indicator of the state of consensus on a presidential nominee."
According to their analysis, Romney's share of the endorsements has also been increasing dramatically.
Three months ago, he had 22 endorsements from members of the GOP establishment, compared with 59 today; his portion of the endorsements has gone from 46 percent to 65 percent.
Perry is the candidate with the most endorsements after Romney (including a sought-after one from Arizona Sheriff Joe Arpaio – though observers noted at the time that Arpaio's approval may do as much harm as good for Perry). In the HuffPost analysis, he has 16 (18 percent of them), compared with just 8 for Gingrich.
Moreover, the HuffPost looks at past candidates who went on to win the nomination, and their share of endorsements at this point in the election season. Romney's dominance, according to that analysis, now exceeds or matches that of other recent Republican presidential nominees.
Of course, there are still plenty of people Romney won't be able to win over.
Erick Erickson, the influential conservative blogger at RedState.com, noted Tuesday that he has yet to give his endorsement – but went on to explain why he thinks any of the remaining candidates (except, perhaps, Paul, whom he fails to mention) would be better than Romney.
The anyone-but-Romney contingent still feels strongly – but if enough of the rest of the GOP establishment lines up behind him, will it matter?