A Reuters/C-SPAN/Zogby poll showed Obama with a 10-point edge on Clinton in the state, 39 percent to 29 percent, as he rode a wave of momentum from his win in Iowa.
McCain was relegated to the political scrap heap last summer after sinking polls and poor fundraising forced him to shake up his staff and recalibrate his campaign, but he now leads Romney by 5 points in New Hampshire.
Clinton and Romney are both under pressure to revive their campaigns after disappointing showings in Iowa, and a second consecutive loss for either could be devastating.
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Romney, who at one time led polls in Iowa and New Hampshire, finished second in Iowa to former Arkansas Gov. Mike Huckabee.
A wealthy former venture capitalist who has pumped tens of millions of his own money into the race, Romney said he was buoyed by a Sunday night debate where he tangled with McCain and Huckabee over their records on taxes and immigration.
"Right now it's a neck-and-neck race. But with the debate last night and the support I received from that debate I anticipate winning tomorrow," Romney said in Stratham.
Edwards, on a 36-hour campaign marathon around the state ahead of Tuesday's vote, said he was the underdog but planned to spring a surprise. A third-place finish would not drive him out of the race, he told reporters.
"I am in this race through the convention and through the White House. I have no intention of stopping this fight that is the cause of my life," he said.
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