In U.S. presidential politics, the focus is on Republican White House contender Herman Cain. Cain says he is reassessing his campaign in the wake of allegations of an extramarital affair, which Cain denies. Meanwhile, the Republican field is looking more like a showdown between former U.S. House of Representatives Speaker Newt Gingrich and former Massachusetts Governor Mitt Romney.

A day after Cain told aides that he is reassessing his presidential bid, the Georgia businessman appeared defiant at a campaign stop in the Midwestern state of Ohio.

"The voice of the people is more powerful than the voice of the media," said Cain.

Cain is denying allegations of an extramarital affair with Ginger White, who told ABC television's Good Morning America program that she was involved with Cain on and off during a 13-year period.

"It was a very casual affair," said White. "I've received gifts and money for the last 2.5 years consistently. This was not sex for cash."

The allegation of an affair comes in the wake of sexual harassment allegations leveled at Cain by four women a few weeks ago, which led to a loss of support in public opinion surveys.

The Republican contender who is gaining at the moment is former House Speaker Newt Gingrich, who leads the eight person nomination race in several national public opinion polls.

"I don't claim to be the perfect candidate," said Gingrich. "I just claim to be a lot more conservative than Mitt Romney and a lot more electable than anybody else."

Cain's drop in the polls seems to have helped Gingrich, who has emerged as the main alternative to former Massachusetts Governor Mitt Romney.

Romney has long been considered the frontrunner in the Republican race, and he continues to focus most of his attention on President Barack Obama, as he did at a campaign stop in the Southern state of Florida.

"President Obama is a nice guy," said Romney. "But I don't think he understands America. I don't think he understands our economy. I don't think he understands the power of free people, free to choose their course in life."

Political strategist Matthew Dowd, an analyst for ABC News, sees the Republican race evolving into a two-man field.

"I think right now that anti-Romney vote is coalesced around the former speaker," said Dowd. "I think more of these votes go to Newt Gingrich, and I think Newt Gingrich is a force that Mitt Romney has to reckon with."

Analyst Stuart Rothenberg, publisher of The Rothenberg Political Report, says Mitt Romney's main challenge remains winning over Republican voters who doubt he is a true conservative.

"The one thing that is consistent is that Mitt Romney is in the top tier, that Mitt Romney appeals to about one-quarter of all Republicans and that he has built a large, established, experienced, national presidential campaign," said Rothenberg. "Whether that will be enough to get the nomination, we don't yet know."

The first test of the 2012 Republican race is less than five weeks away, when voters in the Midwestern state of Iowa hold caucus meetings on January 3 to express their preferences in the eight-candidate Republican field.