The sexual harassment allegations against Herman Cain — a top contender for the U.S. Republicans' presidential nomination — seem to be rallying his right-wing base but could lose him support among the party's moderates.

The forceful early reaction to the Cain firestorm — fuelled by racially charged rhetoric — suggests the Georgia businessman's attempt to cast himself as a victim of the news media and liberals is, so far, paying dividends among his more conservative supporters, who will hold considerable sway in selecting the party's nominee.

But the accusations against Cain, which he denies, may give more centrist Republican voters pause and could cause would-be donors to shy away even as Cain works to capitalize on his rising poll numbers.

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Supporters liken the harassment allegations against Cain, left, to the ones that dogged U.S. Supreme Court Justice Clarence Thomas. (Reuters)

Supporters liken Cain's troubles to those of U.S. Supreme Court Justice Clarence Thomas, another prominent black conservative who also faced sexual harassment allegations during his explosive Senate confirmation hearing two decades ago.

And it's not the first time Cain has had to explain himself since his quick climb in the polls. The political newcomer — a former pizza magnate — had a series of fumbles and has had to clarify comments on abortion, immigration and terrorism suspects.

Cain is again on the defensive after a report on the website Politico that said the U.S. National Restaurant Association gave financial settlements to at least two female employees who had accused him of inappropriate sexual behaviour when he was its chairman.

The Milwaukee Journal Sentinel newspaper, meanwhile, reported that Cain allowed a tax-exempt charity to illegally provide money to help his presidential campaign get started. Cain's chief of staff, Mark Block, says the campaign has asked a lawyer to review the transactions.

Flip-flops on payouts

On Monday, the candidate acknowledged that he had been accused of sexual harassment in the 1990s while he was head of the restaurant trade group, but said the allegations were false. He has, however, given varying responses to questions about whether there were financial settlements with the women who brought the complaints.

Cain spent Monday in Washington, answering questions about why the restaurant trade group he once led paid to settle sexual harassment complaints against him. He planned another day in Washington on Tuesday, trying to quiet concerns that could drag down his meteoric rise in polling.

Cain, who is best known for his management of a pizza restaurant chain, stunned the U.S. political establishment with his rise from national obscurity to place at or near the top of surveys in early nominating states for the Republican presidential candidacy. He is competitive with former Massachusetts governor Mitt Romney, long considered the front-runner for the nomination.

Cain has been pointing to his long record in business to argue that he has the credentials to be president during a time of economic hardship — a small government, anti-tax message that has struck a deep chord with conservatives.