Front-running Republican Presidential candidate Mitt Romney, under pressure from his opponents to disclose his U.S. tax payments, disclosed on Tuesday that he pays a lower tax rate than many Americans.

Mr. Romney emerged largely undamaged in a Monday night debate among a shrinking field of party hopefuls. But the multimillionaire was cornered on the issue of revealing his tax returns.

He agreed to decide on allowing voters to examine his latest tax documents in April, the month when all Americans are required to file tax reports with the federal government.

“I have nothing in them that suggests there’s any problem and I’m happy to do so,” he said. “I sort of feel like we’re showing a lot of exposure at this point,” he added.

On Tuesday he offered a snippet of his personal tax picture, disclosing that he pays an income tax rate close to 15 per cent well below the 35 per cent applied to the nation’s top earners because his income mostly comes from investments. Investment earnings, or capital gains, are taxed at a lower rate than wages and other income in the U.S.

Candidates for high office in the United States are not required to make their tax filings available to the public, but they routinely do so as a good-faith effort to show their sources of income and assessments paid to the government.

Mr. Romney, who formerly headed Bain Capital, a private equity firm, has emphasised his business acumen as a reason he believes he can defeat Democratic President Barack Obama in the November election. The President is vulnerable because of the weak U.S. economy and high joblessness.

But Mr. Romney, the former Governor of Massachusetts, also has to worry about public perception that his wealth buys him special privileges, including in the way his taxes are assessed.

Polls show Mr. Romney as the clear favourite in conservative South Carolina, which holds its primary on Saturday, despite the mistrust or ambivalence of Republican voters who are unhappy with Mr. Romney’s past stands on social issues like abortion and gay rights. Earlier this month, he won the Iowa caucus vote and the New Hampshire primary.

Newt Gingrich, the former speaker of the U.S. House of Representatives, has virtually conceded that a victory for Mr. Romney in the first-in-the-South primary in South Carolina would assure his nomination. That’s why he’s holding little back as he goes for broke against Mr. Romney in hopes that a strong showing in South Carolina will re-energise his White House bid.

On Tuesday, Mr. Gingrich levelled a forceful new attack on Mr. Romney, calling Bain Capital “exploitive.”

Mr. Gingrich had attacked Mr. Romney’s firm before, but his comments before a gathering of business leaders in Columbia, South Carolina, contained some of his harshest rhetoric yet. Mr. Gingrich said that, in at least some instances, the Bain model has meant “leverage the game, borrow the money, leave the debt behind and walk off with all the profits.”

“Now, I’ll let you decide if that’s really good capitalism. I think it’s exploitive. I think it’s not defensible,” he said.

Mr. Gingrich has faced rebuke from some conservatives who accuse him of attacking the Republican bedrock of free enterprise in his criticism of Mr. Romney’s record at Bain. But he argued on Tuesday that raising questions about Mr. Romney’s track record at Bain should not be confused with an attack on capitalism.

Mr. Gingrich gained an endorsement of sorts from former Alaska Gov. Sarah Palin, the party’s Vice-Presidential nominee in 2008. The Fox News contributor told the network on Tuesday night that she would vote for Mr. Gingrich in the South Carolina primary if she could in order to extend the Republican primary race and help the candidates become fully vetted.

“Iron sharpens iron, steel sharpens steel,” Ms. Palin said. “In order to keep this thing going, I’d vote for Newt.”

Also still in competition for the Republican nomination are former Pennsylvania senator Rick Santorum, Texas Governor Rick Perry and Texas Representative Ron Paul.

Mr. Santorum, who finished in a virtual tie with Mr. Romney in the Iowa caucuses, released a new TV ad that compares Mr. Romney to Mr. Obama by claiming that both supported Wall Street bailouts, similar health care reform plans and are liberal on social issues.

The ad then asks: “Why would we ever vote for someone who is just like Obama?”

Mr. Santorum urged South Carolina conservatives to coalesce around one of their own or face Mr. Romney as the Republican nominee.

“He’s got a lot of money, but he doesn’t have the convictions, the authenticity nor the record that is necessary to win this election,” Mr. Santorum told voters. “Please consolidate.”

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