When Mitt Romney launches his second presidential campaign Thursday on a rolling New Hampshire hayfield, notably absent will be a number of endorsers, donors and advisers from his 2008 bid who, for personal and professional reasons, have not committed to his 2012 effort.

After running what was widely considered an unfocused and bloated campaign in 2008, the former Massachusetts governor is returning to the presidential sweepstakes with a more tightly knit team. But his new world isn’t entirely by design: Some of the people who surrounded him in 2008 said they have begged off Romney 2.0 because, as much as they like and respect him, they are not convinced he can survive the Republican primary and beat President Obama.

Some of the doubters are consultants whom Romney has not hired again or who took roles with rival campaigns. But the more prominent Romney refugees are elected officials and GOP bigwigs who are publicly questioning whether Romney has learned the lessons of his failed bid and whether he will be able to connect with voters.

“I was proud to be with Governor Romney, but I also am interested in hearing from the other candidates,” said Ovide Lamontagne, a New Hampshire politician who has had many of the contenders over to his home for coffee and dinner. “I’m looking to identify the most conservative candidate who can win. This is a different election than in 2008.”

Romney has a more robust network — particularly among major donors and establishment figures — than any other Republican in the running. His core team remains largely unchanged from 2008, with longtime advisers Beth Myers, Eric Fehrnstrom, Russ Schriefer and Stuart Stevens, as well as newly elevated campaign manager Matt Rhoades and political director Rich Beeson, calling the shots at headquarters.

“We are a leaner but stronger organization,” campaign spokeswoman Andrea Saul said.

But beyond the inner circle, there has been significant turnover among Romney’s surrogates and advisers, particularly in the early voting states. Many elected officials who endorsed him in 2008 are staying on the sidelines until the contours of the 2012 race become more clear — feeding the notion that Romney is a weak front-runner.

The Democratic National Committee highlighted the issue on Wednesday, creating an online yearbook of “Romney defectors.”

“People make a commitment for a period of time and then they reserve the right to change their mind,” said Tom Rath, a senior Romney adviser based in New Hampshire. “Obviously you’d like to have everybody, but . . . there’s a degree of churning that’s inevitable.”

Bruce Keough, who oversaw Romney’s 2008 New Hampshire campaign, turned down an offer to join the 2012 team. “I don’t think the voters are looking for somebody who’s going to be recasting himself,” he told Mother Jones magazine in May, adding that Romney causes people to think, “Wait a second, I thought I knew him and now I’m not so sure.”

In Iowa, Romney’s 2008 state chairman, Doug Gross, is neutral. So is Gentry Collins, who was Romney’s Iowa director but is not planning to join any 2012 campaign. And Nicole Schlinger, who coordinated Romney’s grass-roots efforts there, was recently hired by former Minnesota governor Tim Pawlenty’s campaign.

“A lot of folks think of him as a very intelligent, capable, successful strong guy who could potentially be a great president, but we didn’t win last time,” Gross said. “There’s a legitimate question as to the extent to which Governor Romney can connect with voters in a way that will allow him to be both a successful candidate and a great president.”

Gross said he will announce an endorsement by the end of June. He said his decision will be influenced in part by whether Romney intends to compete aggressively in Iowa’s first-in-the-nation caucuses.

In South Carolina, which is third on the 2012 calendar, Romney’s highest-profile backer is state Rep. Nathan Ballentine. But in 2008, Romney counted U.S. Sen. Jim DeMint (S.C.) as a senior adviser and scored endorsements from two key state legislators: Nikki Haley, now the governor, and Mick Mulvaney, now a freshman congressman.

This time, the three are neutral and have shown no signs of coming on board. Indeed, Haley has recently criticized the health-care law Romney signed as governor, saying: “We do not want a Massachusetts health-care plan in South Carolina.”

Romney talks regularly with DeMint about budget and economic matters, a Romney adviser said, but publicly, DeMint has kept his distance.

Romney was an early backer of Haley’s in the 2010 governor’s race, endorsing her a month before former Alaska governor Sarah Palin did so, back when she was trailing in the primary polls. That Haley has not endorsed Romney has “got everybody’s eyebrows up a little bit” within the campaign, said a strategist close to Romney’s political and finance operation.

Two Romney veterans, strategist Phil Musser and former Minnesota congressman Vin Weber, have joined Pawlenty’s campaign in senior roles. Both said they parted with Romney amicably.

“I think the world of him,” Weber said. “But I had to make a very personal decision. Tim Pawlenty’s been a friend of mine for 20-plus years. . . . Pawlenty represents our best shot to win in 2012.”

Warren Tompkins, a longtime South Carolina operative, became Romney’s senior adviser in November 2006. Not so this time.

“They have been slow to reach out to people who were with them in the past, in some respects making assumptions that people who were with them last time would be with them this time,” said Tompkins, who has not backed any campaign. “Sometimes you can be a little penny-wise and pound-foolish.”

When Romney formally announces his campaign at the Bittersweet Farm in Stratham, he will be joined by some new supporters, including the farm’s owners, Doug and Stella Scamman. Romney has also won over two key backers of Sen. John McCain in 2008, state Sen. John S. “Jack” Barnes Jr. and Merrimack County Sheriff Scott Hilliard, as well as state Senate Majority Leader Jeb Bradley, who remained neutral in 2008.

Also expected at the farm is former governor John H. Sununu. But he has made no endorsement because he is reportedly torn between Romney and Pawlenty — and waiting to see if the field changes again.