Romney, with 43 percent support in the latest Suffolk University7NEWS poll, has triple the popularity of his nearest opponent, Rep. Ron Paul. He relished the moment at a high school in Manchester that sported nearly as many reporters and cameras as voters.
"You think we can get more than an eight-vote margin here in New Hampshire?" Romney joked about his slim victory in Iowa over former Pennsylvania Sen. Rick Santorum. "I'm going to try. Think we can get there? I sure hope so."
McCain, who won New Hampshire's support in 2000 and in 2008, pitched Romney his former rival with whom he brutally fought in 2008 as the best GOP candidate to beat President Barack Obama.
"I'm here for one reason and one reason only and that is to make sure that we make Mitt Romney the next president of the United States of America and New Hampshire is the state that will catapult him on to victory," McCain said to a rousing applause.
The endorsement is a blow for former Utah Gov. Jon Huntsman, who was one of McCain's first backers in his 2008 presidential campaign and who now employs several of McCain's former campaign staffers in Huntsman's own White House bid.
Asked by The Salt Lake Tribune about the endorsement, Huntsman said he has "great regard" for McCain "I love the man" but the move wouldn't matter with voters.
"It's another example of the establishment piling on," Huntsman said. "And it seems the more the establishment piles on [former Sen. Bob] Dole, McCain and all the rest nobody cares. Nobody cares about this."
At the moment, though, it appears fewer voters are caring about Huntsman, either.
The Suffolk poll shows Huntsman dropped three points to 7 percent in New Hampshire after rising earlier this week to a high of 13 points. The tracking survey showed Huntsman losing self-identified moderates, with only 11 percent of them backing his campaign compared to 17 percent just days before.
Huntsman, playing the optimist, said he didn't have to win New Hampshire, just get above what everyone is expecting, and he noted that Iowa showed a Republican base that isn't satisfied with the current front-runners.
"There is a very unsettled Republican electorate," Huntsman said. "Basically, you've got 75 percent of the party as stated by Iowa that is still looking for an alternative. That means there's a whole lot of blue sky."
Santorum, suddenly thrust into a leading spot after suffering on the far edge of the polls and the debate stage, entered a hall in Brentwood, N.H., on Wednesday, that was so packed, aides feared the fire marshal would shut it down.
Santorum quickly launched into a veiled hit on Romney, arguing that voters shouldn't just go for the "pyrrhic" victory, but pick someone who stands for something and acts on his promises.
"Don't settle for someone who can win but then can't do, won't do, who has no track record of doing things that are necessary to change this country," Santorum said.