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As voters head to the polls Tuesday in New Hampshire for the first-in-the nation Republican presidential primary, expectations count nearly as much as actual votes, leading rivals to question not whether frontrunner Mitt Romney will win but by how much.

It would be difficult for Romney to exceed expectations since he's polling nearly 20 points ahead of his closest competition. But a poorer-than-expected showing means Romney could be vulnerable. And that's what his opponents are counting on.

"The biggest story today is going to be how much Governor Romney falls short of any kind of reasonable expectation because he's been living here, literally bought a house, was the governor next door for years," said Romney rival Newt Gingrich. "And people expected this to be his fortress. I think it's not going to be much of a fortress."

"My sense is he's not going to get anywhere close to 50 percent, and this is his third best state after Utah and Massachusetts so if he can't come close to 50 percent here, it's very unlikely that he can sweep the nomination," Gingrich said later.

For many pollsters, Romney must win with about 37 percent of the vote to match the definition of blowout required by those evaluating the former Massachusetts governor's campaign.

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    While Romney's polling has been slipping in the past week, the Suffolk University/7News tracking poll Tuesday showed Romney polling at 37 percent, nearly 20 percentage points over his next nearest competitor, Ron Paul.

    According to the poll of 500 likely voters surveyed over Sunday and Monday, Romney earned 37 percent over Paul's 18 percent while Jon Huntsman gained 16 percent, Rick Santorum garnered 11 percent, Newt Gingrich took 9 percent and Rick Perry and Buddy Roemer, who hasn't registered high enough in the polls to qualify for the debates, each earned 1 percent.

    Seven percent are undecided.

    "Mitt Romney may beat his closest competitor by a two- to-one margin," said David Paleologos, director of the Suffolk University Political Research Center in Boston, noting that the race is really for second place.

    Andy Smith, a pollster for the University of New Hampshire's Survey Center, told Fox News that anything below 35 percent for Romney could be perceived as a weakness that his opponents can exploit, especially since 78 percent of those surveyed in the latest WMUR/UNH poll said they expect Romney to win on Tuesday.

    Smith said managing expectations -- and making sure that supporters actually go to the polls -- is Romney's biggest challenge.

    But Pollster Frank Luntz, a Fox News analyst who has been tracking audience reaction during the debates, said he's never supported the "conventional wisdom" that Romney has to win with 37 percent of the vote or better before heading into South Carolina, which votes on Jan. 21.

    "As you know, the conventional wisdom is usually wrong," Luntz told Fox News.

    He said all Romney has to do is win by double digits because South Carolina is not going to make the decision based on New Hampshire's vote.

    "They're going to make the decision based on the Fox News debate that's coming up in a week," Luntz said in a plug to the Jan. 16 debate being held in conjunction with the South Carolina Republican Party.

    Managing expectations about his own performance, Santorum told Fox News on Tuesday that he would be pleased to end up in the middle of the pack in this state.

    "That would show we have the momentum," Santorum said, adding that if he outperforms expectations, eventually the race will be cobbled down to two people, himself and Romney.

    "When that happens, game will really be on at that point because then conservatives will have a choice and I am very confident we'll pull this race out," he said.

    Huntsman, who is also trying to surpass expectations and could pull a strong third, is trying to score high by reaching beyond the GOP to registered independents who are allowed to vote in the GOP primary.

    But Pat Caddell, a Democratic pollster for Jimmy Carter and a Fox News contributor, and Alice Stewart, a Republican strategist, said that strategy won't get Huntsman past the Granite State if he's unprepared for the next leg of the race.

    "Candidates have to be strategic, they have to pick and choose which states are more in tune with their views and values and Hunstman did a smart play by putting all of his resources in New Hampshire," said Stewart, a former communications director for Rep. Michele Bachmann, who dropped out of the race after a last-place showing among competing candidates in Iowa.

    "But the key is to make sure he's got the organization and ground game right after New Hampshire," she said.