Republican Mitt Romney was riding high Friday, the eve of Nevada's presidential caucuses, after a new poll gave him a 20-point lead and real estate mogul Donald Trump endorsed his candidacy.

The former Massachusetts governor, who scored a major win in Florida on Tuesday, was back on track after stumbling with an ill-judged remark about poor Americans, as the new poll gave him a huge lead over rival Newt Gingrich.

The survey of likely Republican voters had Romney on 45 percent and Gingrich only 25 percent in the western battleground state, which holds caucuses on Saturday as the race for the Republican nomination spreads west.

But in a new development, Gingrich announced possible party appeal action over the results in Florida, where Romney won big, in theory claiming all its 50 delegates. Gingrich said the delegates should be awarded proportionately.

The developments came as Romney, who has an estimated $250 million fortune, won the endorsement of real estate mogul and celebrity TV star Trump, who briefly flirted with a presidential run last year.

"Mitt is tough, he's smart, he's sharp. He's not going to allow bad things to continue to happen to this country that we all love," Trump said. "Governor Romney, go out and get 'em. You can do it."

Romney, whose campaign has been plagued by a string of wealth-related gaffes and issues, betrayed no qualms about accepting the support of a super-rich benefactor at a glitzy Las Vegas press event.

"There are some things that you just can't imagine happening in your life. This is one of them. Being in Donald Trump's hotel and having his endorsement is a delight," he said, with wife Ann and Trump standing alongside.

Romney, 64, came second in the first Republican contest in Iowa, then swept the second contest in New Hampshire before Gingrich, 68, thumped him South Carolina in mid-January.

Gingrich's support, however, sank fast in the larger and more diverse state of Florida, and Romney now has all the momentum.

But Gingrich, a former House speaker, signaled in Las Vegas that his backers may challenge the Florida results.

"I'm told by the lawyers that it's pretty clear, that it's supposed to be proportional," he told Fox News television.

"That means that Romney's advantage, instead of being 50 delegates, will be about a net of 10, and that makes a huge difference. I suspect it'll be a fight," he said.

Romney pitches himself as a successful entrepreneur with the business acumen to create jobs and turn around a US economy he claims has been ruined by the policies of Democratic President Barack Obama.

But critics say he is a son of wealth and privilege who spent much of his business career in the cut-throat world of venture capital and had a questionable record as a job-creator when he was governor of Massachusetts.

Only last April, Trump painted Romney as a corporate vulture during his time at Bain Capital, the venture capital firm where he made his millions.

"He'd buy companies, he'd close companies, he'd get rid of jobs," Trump said in a CNN interview.

Romney, one of the wealthiest individuals to ever seek the country's highest office, could struggle to connect with ordinary Americans hit hard by the 2008 economic collapse.

He triggered immediate criticism for a comment on Wednesday about America's poorest citizens, which threatened to slow his growing momentum.

"I'm not concerned about the very poor. We have a safety net there. If it needs repair, I'll fix it," he told CNN.

Nevada Republicans hold caucuses on Saturday to pick 28 delegates to the Republican National Convention in the first of the party's nominating contests in the western United States.

Romney, who won handily in Nevada in the 2008 White House race, can expect a boost from fellow Mormons. Four years ago, 26 percent of Nevada Republican caucus voters were Mormon and 95 percent of them backed Romney.

The Nevada poll, carried out by the Las Vegas Review-Journal newspaper and 8NewsNow, showed former senator Rick Santorum trailing with 11 percent and Texas congressman Ron Paul with nine percent.