RALEIGH – The key to interpreting the results of the authoritative Des Moines Register poll is to look past the topline numbers – Mitt Romney at 24 percent, Ron Paul at 22 percent, and Rick Santorum at 15 percent – to the underlying trends, remembering that the topline numbers represent the average voter sentiment over four days last week.

While it’s important to keep in mind that each day’s sample is relatively small, it’s likely that these trends are real: Mitt Romney is in a strong position, Rick Santorum is surging towards a possible upset, and Ron Paul is fading a bit. As the Register’s Kathie Obradovich put it in a Saturday blog post:

The Register’s pollster, J. Ann Selzer of Selzer & Co., said Saturday that she can’t remember seeing such a dramatic surge for a previous caucus candidate in the final days of polling. Santorum started at 10 percent on Tuesday night among likely GOP caucusgoers. He rocketed to 22 percent by the end of polling Friday, just 1 percentage point behind Mitt Romney. The four-day average puts him in third place at 15 percent, but he’s on fire, while Romney has held steady and Ron Paul has gone cold.

What’s going on here? Here’s what I think.

First, whatever you think of Ron Paul’s noninterventionist views on foreign policy, they are not popular among Republicans and GOP-leaning independents in Iowa. (They are even less popular among such voters in future battlegrounds such as South Carolina and Florida.) Over the past week, candidates or surrogates from the other campaigns have hammered Paul on his views, driving uncommitted voters away from him.

The subject matter is different, but Paul has essentially met the same fate as Newt Gingrich did before him. Voters just tuning into the race liked both men during the debates. But attack ads work. Both men had vulnerabilities in the Iowa contest – of apostasy and personality – that their rivals exploited. Add in the fact that Ron Paul seems oddly missing in action on the key fiscal challenge facing the country, and you see why the GOP base may be having second thoughts about him.

As for Santorum, the media spin is that his breakout is the result of months of consistent, onerous campaigning from one side of Iowa to the other. That may have helped a bit, but I suspect the more important cause for the Santorum surge is that he is basically the last man standing.

All the other potential non-Mitts – Michele Bachmann, Rick Perry, Herman Cain, Gingrich, now Paul – have either blown it on the national stage or been subjected to lots of adverse media coverage and negative advertising. Santorum really hasn’t. Respondents in the Des Moines Register poll were rather vague when asked what was driving them towards Santorum. I think that is because these new Santorum voters don’t really know much about him. But they have soured on the other alternatives, and can’t bring themselves to vote for Romney (though many still believe he is the eventual nominee).

Lastly, the former Massachusetts governor has benefited from a number of lucky breaks this year. A crowded field throughout the summer and fall meant no single rival to pull together conservative primary voters who distrust Romney. Each alternative has crashed and burned in turn. Romney surrogates certainly played a role, but for the most part the candidates inflicted the mortal wounds on themselves.

After Gingrich began to fade last week, pundits and occasionally Romney supporters themselves began to set expectations too high for him. They talked of a likely win in Iowa, despite the fact that most of the polls put his small leads well within the margin of sampling error. A second- or even close third-place showing Tuesday night would have done damage to Romney given such expectations.

The Santorum surge has dispelled those expectations. He could win. So could Romney, or even Paul. But the well-financed Perry and the experienced Gingrich both seem out of contention in Iowa. Whatever the order of the finish tomorrow night, that’s good news for Romney.

Hood is president of the John Locke Foundation.