Ten days before the first votes in the 2012 Republican presidential race, Mitt Romney's well-funded campaign machine has held off the most serious challenge to his White House bid and is keeping him near the top of the pack.

The denting of his main rival, Newt Gingrich, endorsements from respected Republicans and a series of well-received media interviews over the past couple of weeks have boosted the former Massachusetts governor's campaign.

The usually buttoned-down Romney also showed a lighter side with an appearance on Monday on comedian David Letterman's late-night talk show.

Gingrich had overtaken Romney in some Iowa polls earlier this month, but a wave of negative television ads by the Romney campaign and his political allies on the
former U.S. House of Representatives speaker has righted the ship.

Restore Our Future, a super political action committee (PAC) fundraising committee formed in large part by close associates of Romney, has spent $2.6 million in the past two weeks on advertisements opposing Gingrich, whose lead in the polls in Iowa has melted.

Romney's failure to move above the 25 percent mark in national opinion polls throughout the year is a problem. But if Gingrich's support collapses in Iowa, which holds its nominating contest on Jan. 3, Romney could have a respectable showing and pick up momentum going into the Jan. 10 New Hampshire primary.

Texas Congressman Ron Paul holds a narrow lead over Romney in most Iowa polls, with Gingrich having slipped to third.

"Wonder why Gingrich's numbers are falling in Iowa? Romney (and Super PACs supporting him) are outspending Gingrich 34:1 this week," noted the Democratic strategy firm Anzalone Liszt Research.

Long-time Romney adviser Eric Fehrnstrom told Reuters that Romney's campaign, by far the best-funded among the Republican candidates, had been ready for a tough December.

"We always thought it would be more competitive and more intense as voting approaches," he said. "But we like the state of the race right now. Momentum is on our side."

Romney largely side-stepped a political capitulation by House Republicans this week over a two-month extension of a payroll tax cut, describing it as part of the "Congressional sausage-making process." And after looking shaky against Gingrich and Texas Governor Rick Perry in debates, Romney has refocused his attacks on President Barack Obama's economic record.

But some voters are starting to take issue with Romney's persistently bleak assessment of the U.S. economy, especially in New Hampshire where conditions are improving. Several small business people enthusiastically volunteered upbeat assessments of their companies this week.

"I think he used facts selectively," said Ken Allen, a restaurant manager from Northfield.

Morey Stettner of Portsmouth pointed out at a townhall meeting with Romney in Conway that the unemployment rate was falling. "The news every day is of a turnaround," Stettner said.

Iowa push

Romney's team has been ambivalent all year toward Iowa. It did not, for example, participate in a straw poll in August that took the Republican presidential pulse of the conservative Midwest state.

However, an endorsement from Iowa's statewide newspaper, the Des Moines Register, has increased the incentive to go for a win there, while publicly keeping expectations low.

Romney has a solid organizational structure in the state that has held together since his first presidential bid in 2008 and he will campaign in some eight cities there over four days
next week.

When Gingrich on Wednesday announced the support of House speakers from Iowa and New Hampshire, Romney's campaign fired back with endorsements from no less than seven former House speakers from the two states. He also won the backing of former
President George H. W. Bush.

As much as Iowa seems a toss-up, New Hampshire is Romney's state to lose, and he needs to post a big win there to silence his critics and build momentum for other contests.

Polls in the New England state consistently show Romney up by double digits over Gingrich, Paul and former Utah Governor Jon Huntsman. A narrow victory for Romney, who owns a home in New Hampshire, could be spun by opponents as a defeat for him as the campaigns head to South Carolina.

"There have been elections in the past where a candidate has been a distance second, but won a moral victory," said Christopher Galdieri, a politics professor at Saint Anselm College in Manchester.

Former New Hampshire Governor John H. Sununu, a close Romney associate, often says that "Iowa picks corn. New Hampshire picks presidents." Sununu was constantly at Romney's side during this week's campaign swing through the Granite State.

"Yes, I am confident," Sununu told Reuters, referring to Romney's chances winning the state and continuing on to the nomination. "It all starts here. The numbers we are seeing
are good numbers."

Even though no votes have been cast, pundits argue about what would benefit Romney most: quickly locking up the nomination so he can concentrate on the November
election against Obama, or enduring a longer, bruising race that would battle-harden him.

Political observers have noted that Romney has bristled at times in television interviews, and can lose focus when challenged.

On Thursday night, at a town meeting in Conway, he sounded irritated and made a sweeping and risky promise to college student Kallie Durkit, who questioned whether Romney had answers for young Americans worried about the job market.

"What I can promise you is this - when you get out of college, if I'm president you'll have a job. If President Obama is re-elected, you will not be able to get a job," Romney said.