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Of the past six contested Republican caucuses, only three winners have ended up clinching the nomination: George W. Bush, Bob Dole and Gerald R. Ford, with only Mr. Bush going on to the White House. Former Arkansas Gov. Mike Huckabee notably captured Iowa in 2008, with Sen. John McCain of Arizona going on to win the nomination. George H.W. Bush and Ronald Reagan also did not emerge victorious before ultimately winning the presidency.

Democrats have nearly the same record in Iowa. Five out of the total nine Democratic winners in Iowa have gone on to become their party’s nominee. Two of them — Barack Obama and Jimmy Carter — continued their winning streaks and wound up in the Oval Office.

The success rate has no bearing on whether Iowa should retain its influential status, said David Yepsen, the longtime dean of Iowa political reporters and a professor at the Paul Simon Public Policy Institute at Southern Illinois University.

“The purpose of the exercise is not to predict the winner,” Mr. Yepsen said. “The more important role is winnowing the field. It already winnowed Minnesota Gov. Tim Pawlenty, and Michele Bachmann and maybe even Rick Perry. That’s a function, too.”

Iowa’s median age is almost a full year older than the national average, and its population grew just 4.1 percent between 2000 and 2010, which was less than half the national growth rate, according to Census Bureau statistics.

Its disproportionately white and Christian population also can produce unpredictable but invaluable results, Mr. Yepsen said. Iowa was 3 percent black, 5 percent Hispanic and nearly 2 percent Asian in the 2010 census.

“Over the years, Iowa was criticized because it was too white, but Obama’s win here was able to convince a lot of political folks around the country that he could attract white votes,” he said. “His numbers in South Carolina turned around after this.”

Other Iowans want to keep their early influence out of fear that they will be overlooked down the road in the campaign.

“This is the one chance we have to really make an impact and get to know the candidates,” said Carol Kantman, 66, who was waiting in line to shake Mr. Gingrich’s hand Sunday.

“We do more than just pick corn,” interjected her friend, 64-year-old John Winters, taking a veiled shot at the one member of the Republican field who has explicitly snubbed Iowa.

On Thursday, former Utah Gov. Jon Huntsman Jr. defended his decision to focus on New Hampshire by saying, “They pick corn in Iowa. They actually pick presidents here in New Hampshire.”

Other states’ attempts to reduce Iowa’s influence by moving up their primaries have only served to further compress the nominating process and make Iowa’s role even more important, Mr. Yepsen said.

The Iowa caucuses were originally scheduled to commence on Feb. 6, much later than the date in 2008. But in late September, the Florida Republican Party disrupted the schedule by announcing its intent to move its primary to Jan. 31 and reap the benefits of the candidates’ earliest visits.

The Republican National Committee punished Florida by deciding to deny half its delegates, but Florida refused to change the date.

In response, the Iowa Republican Party, along with New Hampshire, South Carolina and Nevada, then sought to move their caucuses or primaries back into early January. All but Nevada, which agreed to follow Florida, confirmed their caucus and primary dates to take place throughout January, with Iowa in the lead.