Mitt Romney and Newt Gingrich during the Republican presidential debate
The verbal sparring and ad war between Mitt Romney and Newt Gingrich in the Florida primary may be contributing to GOP voters' poor view of the presidential field, according to a Pew Research Center poll. Reuters

The race for the Republican nomination has heated up after a tense televised presidential debate between the four remaining candidates.

Former Speaker of the US House of Representatives, Newt Gingrich, who has made a late rally in South Carolina, was asked about allegations that he had asked his wife for an "open marriage" by CNN moderator John King.

He said: "It is as close to despicable as anything I can imagine. I'm frankly astounded that CNN would take trash like that and ask it to open a presidential debate."

Gingrich received a standing ovation for his reply, which forced the rival candidates to diplomatically avoid the issue.

Reid Epstein, a journalist at Politico, told International Business Times UK: "Whenever a candidate get close to Romney, as we saw with [Herman] Cain, [Rick] Perry and now Gingrich, the vetting process becomes more severe."

Former governor of Massachusetts Mitt Romney, who has had a torrid time in South Carolina with a series of blows to his campaign, made another miscalculation over the issue of his tax returns.

When asked whether his tax returns would be published, the former Bain Capital CEO replied: "Maybe." The crowd booed in response to his answer.

He said: "I don't know how many years I'll release. [Boos] I'll take a look at what the [more boos] what our documents are and I'll release multiple years. I don't know how many years, but I'll be happy to do that."

Recent polls, coupled with Rick Perry's endorsement of Gingrich after he pulled out of the campaign, suggested Gingrich was the candidate with the momentum and Romney the one struggling to validate his standing as frontrunner as the number of contenders vying for the White House narrows down.