For the past five years, Mitt Romney has been making the quick drive from his home in Massachusetts to meet New Hampshire Republicans. In the back of the car, Romney e-mails potential supporters from his iPad. His aides pass out bumper stickers at marathons and chili festivals. Local elected officials backing him spend Saturdays hammering 4-by-8-foot Romney road signs into the crisp countryside.

If Romney has a lock on any state in his quest for the Republican presidential nomination, it’s New Hampshire. All year, most polls have shown the former Massachusetts governor with a 2-to-1 lead over his closest competitors.

Yet, with just seven weeks until the Jan. 10 primary, Romney’s strategists don’t consider New Hampshire a sure bet. New Hampshire’s inveterately independent-minded and mind-changing voters make Romney and his team anxious.

“What makes me nervous is history,” said Tom Rath, a senior adviser to Romney and a longtime presidential strategist in New Hampshire. “It’s like having a five-run lead at Fenway Park. Those leads can evaporate quickly. It’s a hitter’s ballpark, and somebody can always make a run. You’ve got to get all 27 outs.”

“New Hampshire,” Rath added, “is the paradigm of Yogi Berra’s comment, ‘It ain’t over till it’s over.’ ”

Romney is trying to demonstrate momentum here, and will gain an important new supporter Sunday when newly elected Sen. Kelly Ayotte, one of the highest-profile state Republicans who had not backed a candidate, will endorse him at an afternoon rally in her home town of Nashua.

But others are trying to stop Romney’s march to the primary, including former Utah governor Jon Huntsman Jr., who has been logging more time here than any other candidate. On Tuesday, he celebrated his 100th campaign stop, a town hall meeting at the Portsmouth Elks Lodge, where he joked that these days he’s subsisting on lobster rolls and speaking with a local accent. An independent group financed by his wealthy father is blanketing the airwaves with pro-Huntsman advertisements.

One new poll, however, suggests it’s not Huntsman but former House speaker Newt Gingrich who may be in a dead heat with Romney here. The survey, released Friday by Magellan Strategies, had Romney at 29 percent and Gingrich at 27 percent. But it is considered less credible than other polls because it relies on automated phone calls rather than live interviews.

Indeed, Magellan’s findings are out of step with other public polls; a Bloomberg News survey earlier in the week had Romney at 40 percent, followed by Rep. Ron Paul at 17 percent and Gingrich at 11 percent. The Romney campaign’s internal polling also gives him a similarly sizeable lead, aides said.

Asked Friday night if he could beat Romney in the Granite State, the usually confident Gingrich sounded unsure. “Who knows?” Gingrich said. Then he thought about the latest poll and added, “It’s more plausible tonight than it was yesterday.”

Huntsman’s chief strategist, John Weaver, who helped engineer Sen. John McCain’s victory in New Hampshire’s 2000 primary, said that voters here view Romney as “the incumbent” and that there’s an opening for a contender who can build a passionate following before Romney runs out the clock.

“Romney’s biggest vulnerability is that they know him,” Weaver said. “In a year in which the party and the people who are going to be voting in the primary are looking for constancy and someone with a north star, he has neither. They know him to be a calculating, careful politician in a year in which they don’t like that creature.”

Romney isn’t leaving anything to chance. He could have spent this weekend where his opponents have, in Iowa, auditioning before conservatives in the state whose caucuses kick off the nominating contest. Instead, Romney has been making a four-day swing across New Hampshire, fortifying his base with a blitz of rallies, town hall meetings and business tours. He’s become so familiar here that some Republicans are hearing his pitch for the second or third or fourth time.

“I love this country,” Romney told about 100 busi­ness­people who leaned over balconies and a winding staircase to see him Friday in the atrium of a law firm here. “I want to keep it strong. I want to put Americans to work. . . . This is what my passion is. I hope to have your support, and I hope people here in New Hampshire give me the nod to become the Republican nominee — because if I’m your nominee, I’m gonna win.”

Former governor and senator Judd Gregg, a Romney supporter, said he sees no serious threat. “I don’t hear any footsteps,” Gregg said. “You can usually hear when someone comes up from the outside, like John McCain was with George W. Bush [in 2000], but I just don’t hear it.”

In fact, some Republicans predict the real race here is for second place. “I don’t think any other candidate can consolidate support and make a real run at winning in New Hampshire other than Romney,” said former state GOP chairman Fergus Cullen, who is unaligned in the contest. But that isn’t slowing Romney, who attended Friday’s Santa Fund luncheon in Manchester. He sat patiently through a long program but didn’t make a speech. He was at the charity function only to glad-hand.

“Do you vote in the primary?” Romney asked one man.

When the man said he did, Romney told him: “Good. I need your help.”

“There’s a 90 percent chance you’ll get it,” the man replied.

That was good enough for Romney, who turned quickly in search of more help. Extending his hand to another man, Romney, especially animated on this day, introduced himself.

“Best of luck,” the man told him, never revealing how he might vote.

“Thank you,” the candidate replied. “I may need some of that.”