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“If you were a Huckabee supporter four years ago, I think Santorum is the more natural fit for those people than maybe even a Michele Bachmann,” he said. “I think he tends to speak their language.”

Mr. Huckabee’s upset victory took some of the wind out of Mr. Romney’s sails heading into New Hampshire, where Sen. John McCain took advantage of the opening, winning the Granite State’s primary, basically dealing the blows that put Mr. Romney’s presidential hopes on the path to defeat.

More than three years later, Mr. Romney has been the one regular face in the top two slots of the Republican leader board since this summer.

Conservatives, meanwhile, have migrated from Michele Bachmann to Rick Perry to Herman Cain and now Newt Gingrich, who leads in the latest USA Today/Gallup poll of Republican and Republican-leaning voters.

Mr. Robinson said that Mr. Cain and Mr. Gingrich have struggled to deal with national scrutiny. They also haven’t made a big presence in Iowa, he said. Mr. Santorum, though, has visited the state’s 99 counties and established a solid ground operation, which is starting to pay dividends.

“I’m hearing an awful lot of people who are coming around to the idea that Rick Santorum is their guy,” Mr. Robinson said. “Social conservatives who have been engaged throughout the campaign, but are kind of taking a more wait-and-see approach before they get behind a candidate, I think at the end of the day, he is kind of a natural fit for them.”