(AP Photo/Robert F. Bukaty)

WASHINGTON - Republican front-runner Mitt Romney is moving on from a narrow victory in the Maine caucuses to raising money for his already well-financed campaign - and to the more difficult task of convincing Republican voters he is conservative enough to be the party standard-bearer against President Barack Obama.

The slim three-percentage-point win Saturday in Maine over Texas congressman Ron Paul offered little more than a symbolic boost to Romney, the former Massachusetts governor and ultra-wealthy businessman.

Former Alaska Gov. Sarah Palin, a prominent voice among some conservatives, said Romney has work to do to convince Republican voters he's moved beyond his "pretty moderate past ... even in some cases a liberal past."

"I am not convinced, and I do not think the majority of GOP (Republican) and independent voters are convinced," Palin said on Fox News Sunday.

Despite his showing in Maine, Paul is so far not a serious challenger to Romney in the way that the other two candidates - Newt Gingrich, the former speaker of the House of Representatives, and Rick Santorum, a former Pennsylvania senator - are.

Obama is vulnerable in his bid for a second term in the White House in November's election because of his handling of the economic downturn spawned by the near collapse of the U.S. financial system in the final months of the presidency of George W. Bush.

That disadvantage with voters seems, however, to be easing with increasing but tentative signs of a slight acceleration of the economic rebound.

Romney won in Maine, the lightly populated U.S. state in the extreme northeast corner of the country, after three humbling defeats earlier last week to Santorum. He overcame Paul by 39 per cent to 36 per cent. Santorum and Gingrich, who didn't actively campaign in Maine, won 18 per cent and 6 per cent, respectively.

Romney now begins to regroup from the battering he took from Santorum last Tuesday in Colorado, Minnesota and Missouri. There won't be another nominating contest until Arizona and Michigan hold primaries at the end of the month, and the next Republican debate is 10 days away.

Santorum said Sunday he could do "exceptionally well" in Michigan, where Romney's father was governor and the candidate was born.

"We're going to spend a lot of time in Michigan and Arizona, and those are up next. And that's where we've really been focusing on," Santorum told ABC's "This Week." He suggested that a strong showing in those contests would make the presidential contest "a two-man race," dismissing Gingrich and Paul.

Santorum shrugged off his third-place finish Saturday in the caucuses in Maine, where he didn't actively compete. He described Romney's recent criticism - Romney is painting Santorum as a longtime Washington insider who pursued home-state projects - as "desperate."

"You reach a point where desperate people do desperate things," said Santorum, a former representative and senator from Pennsylvania.

Santorum's campaign saw a surge in donations after last week's victories - $3 million over three days - but is unlikely to catch Romney in the money race.

Santorum reported just $279,000 in the bank at the end of December, compared with $19.9 million for Romney. Gingrich had $2.1 million, but is still carrying substantial debt, while Paul reported $1.9 million.

Romney's relative success in Maine - combined with his victory in the presidential straw poll at the Conservative Political Action Committee conference in Washington hours earlier - may help further expand his financial advantage, despite some lingering skepticism among some conservatives.

The narrative coming out of Maine will likely reverberate in the political echo chamber for weeks until the next contests on Feb. 28. Romney hopes it will be more positive than it has been over the past week, arguably his worst of the year.

Paul gave Maine considerable attention in recent weeks. The libertarian-minded Texas congressman has scored a handful of top three finishes in other early-voting states, but his strategy is based on winning some of the smaller caucus contests where his passionate base of support can have an oversized impact.

On what has become a hot-button conservative issue, after three weeks of controversy that pitted the nation's Catholic bishops against the White House, Obama revised his policy Friday on a key health care issue. Instead of requiring religious-affiliated institutions to cover contraception, the policy would now allow their employees to get free contraception directly from health insurance companies.

White House chief of staff Jack Lew defended the decision Sunday, noting that there is no longer room for compromise.

"This is our plan," he said on CNN's "State of the Union."

The focus on social issues plays well for Santorum, who has long been considered a staunch cultural conservative. Those credentials helped fuel his success last week.

Romney's team is preparing an aggressive push against Santorum inMichigan, where Romney is a household name - and where his advisers had hoped for an easy victory. Romney'sfather, George, not only served as governor in the state but was chairmain of now-defunct American Motor Corp. before mounting a failed bid for president in 1968.

Romney leads the overall race for delegates, with 123. Santorum has 72, Gingrich has 32 and Paul has 19. It takes 1,144 delegates to win the nomination.