ROCHESTER, N.H -- . It’s a comment heard over and over again on the campaign trail.

"My main concern is finding the candidate who can beat Barack Obama,’’ said Dave Griswold of Kingston, listening to Rick Santorum in New Hampshire the other day, but thinking Mitt Romney may be tougher against Obama.

"I consider myself a conservative, but I’m a realist,’’ said Chuck Clement, a propane company owner in Rochester. "We need to nominate someone who really can win. Mitt is electable."

Such pragmatism is the reason Romney is marching toward the Republican presidential nomination despite doubts and ambivalence from much of the GOP’s conservative base. He eked out a win in Iowa, where only 14 percent of "very conservative" caucusgoers supported him, but half said their priority was having a candidate who can beat Obama.

But what if conventional wisdom is wrong?

Romney’s rivals are trying, with little success so far, to make the case that nominating him would be a gift to the Democrats.

He’s too cold and plastic, they say. Too many flip-flops. Too wealthy and out of touch. His Massachusetts health care overhaul takes a key issue off the table. He doesn’t offer a sharp-enough contrast with Obama.

"What Republicans have to ask is, who’s most likely in the long run to survive against the kind of billion-dollar campaign the Obama team is going to run?" Newt Gingrich said Sunday in a Meet the Press debate on NBC. "A bold Reagan conservative, with a very strong economic plan, is a lot more likely to succeed in that campaign than a relatively timid, Massachusetts moderate who even the Wall Street Journal said had an economic plan so timid it resembled Obama."

But the knock that Romney is too moderate almost by definition stands to make him best equipped to win over swing voters in the general election.

"He has the ability to unite the base ­­- and appeal to independents," said former Minnesota Gov. Tim Pawlenty, who endorsed Romney after dropping out of the race last fall.

Polls consistently show Romney the strongest Republican against Obama, trailing by just 2 percentage points, according to the average of recent polls compiled by RealClearPolitics.

"That’s just about name ID,’’ scoffed John Weaver, an adviser to former Utah Gov. Jon Huntsman. "Barack Obama may be a terrible president, but he’s a darn good politician. Mitt Romney generates all the excitement of Bob Dole."

A front-page editorial in the Sunday edition of the New Hampshire Union Leader newspaper dismissed Romney as "a nice, rich man with a tin ear."

The question many conservative activists ask is whether a candidate who draws a lukewarm response from the GOP base can motivate Republican voters to turn out in November.

"A big part of the reason Republicans were so successful was the energy of the tea party movement, and Mitt Romney is a sedative to the tea party. He would put it to sleep," said Nelson Warfield, an adviser to the Rick Perry campaign. "It’s very troubling for our prospects if we nominate someone who 75 percent of the party doesn’t want."

But two words may do more to motivate Republican voters than anything else: Barack Obama.

"We’re looking for someone who can beat Barack Obama, and Mitt Romney is the one person the Democrats are most afraid of,’’ said South Carolina Gov. Nikki Haley, a tea party favorite helping Romney in that state’s Jan. 21 primary. "They will unite behind Mitt Romney, especially when they understand he has not been part of Washington."

Republicans suffered from an enthusiasm gap in 2008 when they nominated John McCain, another candidate viewed skeptically by many conservatives. But four years ago, Obama was a fresh face and an unpopular Republican president was winding down his second term.

This year, Republicans are banking on a highly energized electorate fired up to make Obama a one-term president. There’s little evidence so far in the primary contest, however.

Crowds at GOP rallies in New Hampshire have been sedate and often small compared with prior cycles. About 123,000 people turned out for the Iowa caucuses, slightly more than in 2008, but far fewer than expected.

Republican strategist Mike Murphy isn’t worried. "The whole reason we call them the base is because they always vote Republican,’’ he said. "It will be a big turnout election, and if Romney’s the nominee he will certainly have no turnout problem with the right."

During Sunday’s debate, Murphy on Twitter scoffed at Ging­rich’s attack on Romney’s electability: "Crazy opening attack from Newt. He couldn’t carry a swing state even if it were made of feathers.’’

Count Hanover businessman John Patton among those conservatives hoping against the odds that Republicans nominate almost anyone else.

"I’m a conservative, and I don’t believe Romney has any core philosophy. I think he aspires to be president just for personal reasons and not for the good of country,’’ Patton said.

And if Romney is the nominee?

"I’d vote for him over Obama."