Gaining Gingrich is Romney's new challenge

GREENVILLE, South Carolina (Reuters) - Republican front-runner Mitt Romney has a new challenge to contend with as presidential candidates brace for another debate on Saturday -- the rise of Newt Gingrich.

The former speaker of the House of Representatives is gaining in the polls and may represent conservatives' last best hope in 2012 in their search for an alternative to the more moderate Romney, now that Herman Cain and Rick Perry are struggling.

The candidates gather at 8 p.m. at Wofford College in nearby Spartanburg for a 90-minute debate sponsored by CBS News and the National Journal.

The debate, the second in three days, is devoted to foreign policy. The only candidate in the field with any substantial diplomatic experience is former U.S. Ambassador to China Jon Huntsman, whose campaign as a moderate needs a boost.

Iran's alleged pursuit of a nuclear weapon and the possibility Israel may strike Iranian targets suspected of nuclear development are likely to be at the forefront, as well as China's increasingly large role on the world stage.

Gingrich was mired for months in single digits in polls of Republican voters but has recently seen his stock rise as Perry has sagged from poor debate performances and Cain has suffered from sexual harassment allegations, which he denies.

In a CBS News poll released on Friday, Cain was first at 18 percent -- down from 25 percent in late October -- and Gingrich was tied for second with Romney at 15 percent, among Republican primary voters.

In South Carolina, where Republicans vote after early nominating contests in Iowa and New Hampshire, Cain is at 26 percent, Gingrich at 19 percent and Romney at 16 percent, according to an Insider Advantage poll.

Romney, taking reporters' questions at an event near Greenville on Friday, expressed no concern about Gingrich's rise in the polls.

"My responsibility is to go out and tell people why I think I should be the guy who leads the country. If other candidates do well, that's great. That's the nature of a campaign," Romney said.

'SERIOUS POTENTIAL PRESIDENT'

Gingrich told CBS' "Early Show" on Friday that he believed he had shown Republicans his campaign had substance.

"And I think people are looking for a serious potential president because they see the issues as being so very serious to their own lives," he said.

Gingrich has struggled, however, to contain his irritation at the debate moderators, who are typically Washington journalists, making him appear petulant and dismissive.

"I just want to point out my colleagues have done a terrific job of answering an absurd question," Gingrich said to CNBC anchor Maria Bartiromo at a debate on Wednesday when asked how he would fix the U.S. healthcare system.

Republican strategist Jim Dyke said Gingrich was on a surge and may well win Iowa, which holds the first U.S. nominating contest on January 3.

But he said Romney's methodical approach -- strong debate performances and effective campaign organizing -- would eventually pay him dividends.

"With each sort of turn of the anti-Romney crowd, Romney picks up a little bit more, and that's sort of slow and steady," Dyke said.

Mochila insert follows.