Newt shrugs off 'open marriage' jibe to make a last-minute surge

The Republican race was blown wide open today after a surge in support for Newt Gingrich threatened to derail Mitt Romney.

Mr Romney was favourite to win tomorrow's South Carolina primary but after two bruising debates and repeated questioning about his business past, Mr Gingrich is now polling neck and neck.

Two polls put Mr Gingrich slightly ahead in the race after fellow candidate Rick Perry quit yesterday and backed the 68-year-old former Speaker of the House.

Mr Gingrich badly needs to win South Carolina to halt Mr Romney, who has emerged as the clear front-runner to fight the November election.

But allegations about Mr Gingrich's past could still haunt him after his ex-wife gave an explosive interview claiming he lacked the moral backbone to be US President.

Marianne Gingrich claimed her husband asked for an open marriage before their divorce in 2000. She also said the day after he told her about his affair with Callista Bisek - now his third wife - he delivered a speech on family values to a group of Republican women.

"How could he ask me for a divorce on Monday and within 48 hours give a speech on family values and talk about how people treat people?" she said.

At the start of a CNN debate with all the remaining candidates, Mr Gingrich reacted furiously when asked about the damaging allegations. Mr Gingrich confronted moderator John King, who asked about Marianne's claims at the start of the debate.

"I am appalled that you would begin a presidential debate on a topic like that," Mr Gingrich said. "To take an ex-wife and make it, two days before the primary, a significant question in a presidential campaign, is as close to despicable as anything I can imagine."

He added: "I am frankly astounded that CNN would take trash like that and use it to open a presidential debate."

The other candidates - Mr Romney, Ron Paul and Rick Santorum - did not raise the issue during the debate.

All four candidates used the platform to attack President Barack Obama, but first Mr Gingrich and then Mr Santorum challenged Mr Romney over his switch of position on abortion. He now says he opposes abortion.

Mr Romney, former chief executive of Bain & Company, refused to release his income tax returns before tomorrow's vote and was silent over why some of his millions were invested in the Cayman Islands, how much was there or whether any other funds were held offshore.

Experts predict the fight to secure the Republican nomination is now a two-horse race between Mr Romney and Mr Gingrich.

Mr Santorum, who won the Iowa caucus after a recount, still has an outside chance but trails in the polls in South Carolina and Florida, which holds its primary at the end of the month. Ron Paul is expected to finish fourth in South Carolina.