As the astute Ross Douthat points out, the race in Iowa is now between Gingrich and Paul
Right now, the polls show Paul to be in second place, with Romney still fading and everyone else having almost disappeared.
But Gingrich's support is soft and ambivalent, while Paul's is enthusiastic and unwavering. Gingrich isn't organized in Iowa or anywhere else. His surge depends entirely on his professorial excellence in debating and the sense that he's now the most plausible alternative to Romney.
Paul is highly organized in Iowa, and his effort in the state has been disciplined and very personal.
Everyone knows that intensity of support and organization in caucus states are the keys. The turnout, even when relatively high, is much lower than that in primary states. Supporters have to be motivated and encouraged to show up for the long and boring meetings.
In Iowa (and many other states, of course), the most motivated Republicans are disproportionally evangelical and at least friendly to the notorious Tea Party.
Neither Paul nor Gingrich is exactly their kind of guy, although both seem preferable to Romney. They do well in talking for personal freedom and against intrusive government. They both seem more principled than flip-floppy Mitt.
Lots of Republicans (and, I think, the sensible ones) don't think either Paul or Gingrich has any business being president. Both lack the qualities associated with statesmanship or just executive competence. Paul is completely lacking in executive experience, and Newt's quasi-executive performance as speaker doesn't inspire confidence. And then, as Paul constantly points out, there's the issue of how Newt has made his living over the last decade.
Paul's foreign policy is dangerously utopian in its promiscuous advocacy of military downsizing and American withdrawal. Gingrich's blowhard comments about, for example, Palestine being a merely invented country aren't what a president, looking out for the true interests of Israel, would say. But Paul, the fear is, would cut Israel off altogether.
Those thinking that the nomination of Newt would be a disaster are rooting for Paul in Iowa, in the hopes of denying him the perhaps irresistible momentum that would come from a victory. They really don't think that Paul's victory there would be followed up by any others. They're rooting for man who has no business being nominated—and won't be—over another man who has no business being nominated—but might be.
But it's unclear, in truth, what happens if and when Paul wins in Iowa. The Republicans, in general, are in an anyone but Romney mood.
The present nominating process makes it quite difficult—if not quite impossible—for a new candidate to enter the race this late.