Making Romney the nominee “would certainly lead to deep questions about what we stand for and who we are,’’ Gingrich said, speaking to a few reporters in the lobby of his Concord hotel.

Gingrich is among those explicitly challenging Romney’s credentials to lead a coalition of Republicans to the White House and control of the Senate. After stumbling early, soaring in the polls, and appearing to fizzle last month (he finished fourth in Iowa, with 13 percent of the vote), Gingrich is seeking a resurgence by branding Romney a “relatively timid Massachusetts moderate’’ who lacks a commitment to cutting government programs and reducing federal debt.

“Reagan was not as hard-hitting and explicit on some of these social issues as the Tea Party and southern evangelical Christians,’’ he said.

Such voters are averse to compromise, even if it means sacrificing the ability to govern in Washington.

Southern conservatism, which has been gaining influence in the Republican Party for 50 years, gives strength to candidates who appeal to ideological purity such as Santorum and Paul, said James Thurber, director of the Center for Congressional and Presidential Studies at American University.

What the party lacks, say many Republicans wistfully, is another Ronald Reagan to unify and inspire a diverse base. But even Reagan was moderate by today’s Republican standards.

Front-runner Romney has argued all year that he is best-equipped to beat President Obama in November and lead a governing coalition of all three factions. But he lacks broad-based support from conservatives, who want an unwavering commitment to core GOP values. Romney’s rivals have pummeled him as insufficiently conservative in debates and on the airwaves as they seek to exploit that perceived weakness.

New Hampshire Tea Party movement activist Jerry DeLemus has some guidance for debate viewers at home trying to decipher the Republican play-by-play: “You’re seeing a battle between the establishment Republicans who want to retain power in Washington versus Republicans who say we need to correct our course.’’

The extraordinarily close Iowa caucus brought the party’s three-way disputes to the forefront, and the weekend’s debates highlighted the divides leading up to tomorrow’s New Hampshire primary.

The three major factions within the GOP - represented by Santorum and social conservatives; Ron Paul, with his Tea Party movement deficit hawks; and Mitt Romney, backed by the business, government, and foreign policy establishment - are in competition to define what the party stands for.

If that is the standard, the Republican Party has much work to do.

“This election is going to be about who can articulate a vision of who we are,’’ Rick Santorum told college students during a campaign stop in Concord.

CONCORD, N.H. - Republican voters are not just struggling to pick the party’s nominee for president. As the candidates darting to diners and school gyms across New Hampshire frequently proclaim, they are mapping the future of the party.

“The nominee will define us,’’ he said.

Romney is striking Reaganesque notes of his own, hoping to unite the party under a patriotic vision. In one of his TV spots running in New Hampshire, Romney says the 2012 campaign “is an election to save the soul of America.’’ The barrier to that strategy is a lack of faith in his level of conviction.

“I don’t think he’s conservative enough. He’s prochoice, then prolife. He’s very much a politician,’’ said Dave Caron, a Christian conservative and air traffic controller from Danbury. The family’s van was hand-painted with the words: “God,’’ “Jesus,’’ and “Santorum.’’

Paul’s army of insurgents has a strong dislike for the Republican mainstream. The noisy crowd inside an airplane hangar in Nashua cheered heartily when Paul set foot on New Hampshire soil Friday and declared: “They call us dangerous. In a way we are, to their empire!’’

Tea Party movement favorite Senator Rand Paul of Kentucky took the stage before his father and spelled out the mission: “The Republican Party is an empty vessel unless we imbue it with values.’’

To Romney’s advantage, Paul and Santorum lack appeal to broad swaths of the Republican electorate. Paul’s plan to disengage militarily from the rest of the world strikes many voters, even those at his rallies, as unrealistic.

Bigoted comments were published under Paul’s name in his newsletters in the 1980s (the candidate has said he did not know what the newsletters contained). And Santorum’s antiabortion views and opposition to gay marriage signal a religious intolerance that had made it difficult to expand support among moderates.

Said Angelica Martinez, a Smith College student from New Jersey who sat with friends in a booth at the Tilton diner Santorum visited: Romney is “the most relatable out of everyone.’’

History suggests the party rank-and-file will get behind the eventual nominee, whether it is Romney or someone else, united in dislike of Obama. The phenomenon is what Thurber called the “rally effect.’’

Whether such a rally would happen depends on voters in New Hampshire tomorrow, South Carolina next week, and Florida on Jan. 31. Romney’s forces are counting on their superior financial advantages and roster of party endorsements to win a prolonged battle.

If the outcome is not decided after Florida’s election, the next big test of the candidates’ appeal will be Feb. 28, with primaries in Arizona and Michigan, followed a week later by Super Tuesday, when 10 states, including Massachusetts, go to the polls.

“We’ll put our egos and bruised feelings aside and come together and do what’s right for our nation,’’ Romney told a questioner who rose at town hall in Tilton to ask him about party infighting.

A key New Hampshire ally for Romney, Judd Gregg, former senator, bolstered that idea in an interview, saying primary voters will undoubtedly pull together and help Romney get beyond the 25 percent ceiling he has encountered in the Iowa caucus and national polls.

“There’s always a strain in both parties that think ideological purity trumps ability to govern,’’ said Gregg. But that is a small minority of the electorate, he added. “After New Hampshire, that 25 percent thing is history, I think.’’

Christopher Rowland can be reached at crowland@globe.com.

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