GOP candidates bid for late Iowa votes Republican candidates were frantically trying to win over undecided Iowa voters in the final hours before the first ballots were to be cast for the party's nomination to be president, promising a brighter future for America and - in some cases - levelling fierce accusations at one another. In an interview with CBS on Tuesday, Newt Gingrich, the former speaker of the House of Representatives who has slipped to fourth place in the polls under a barrage of negative television commercials, accused his rival Mitt Romney of being a "liar." "I just think he ought to be honest with the American people and try to win as the real Mitt Romney, not try to invent a poll-driven, consultant-guided version that goes around with talking points, and I think he ought to be candid," said Mr Gingrich, who has been pummelled with attack advertisements from groups linked to Mr Romney. I don't think he's being candid and that will be a major issue. For his part, Mr Romney held a rally in downtown Des Moines during which he did not address Mr Gingrich's accusations but directed his criticism at President Barack Obama and promised to revive the US economy. "There is a huge gap between the promises and the delivery," Mr Romney said of Mr Obama. "I want to make America the most attractive place in the world for job growth," Mr Romney said, citing a combination of tax and regulatory reform, higher energy production and fiscal restraint. He also took aim at Mr Obama's policy on Iran, saying he should have pushed for more "crippling sanctions" and sided with the dissidents. With clear skies in the forecast for 7pm, when the caucuses will be held, turnout is expected to be strong, probably exceeding the 119,000 voters who showed up for the Republican contest in the state in 2008. With 41 per cent of voters still undecided last week, according to a Des Moines Register poll, the outcome of the race was highly uncertain. Mr Romney, the former governor of Massachusetts, and Ron Paul, the libertarian Texas congressman, were roughly tied for first place - with Rick Santorum staging a late rally that the former Pennsylvania senator hopes will lead him to a dramatic upset victory. Mr Gingrich, first in the polls just a month ago, has since slipped into fourth place. Diane van Wyk, 48, a social studies instructor at Valley High School, says she is still undecided, torn between Mr Gingrich and Mr Santorum. "It's head versus heart," she says. A win in Iowa is considered a big boon for candidates vying for the presidency, in that it helps build political momentum and fundraising for the rest of the campaign. Conversely, a poor showing in Iowa raises the stakes for a better performance in the next early contest in New Hampshire on Tuesday, and could even lead some candidates to drop out, winnowing the field. Michele Bachmann, the Minnesota congresswoman who led the polls in Iowa over the summer, has seen her support collapse in recent months, and is in danger of stepping away from the race. But at a West Des Moines High School on Tuesday morning, she was still trying to corral votes. I want a future. I want a hope for you, and we can do it," she told a group of first-time voters . Mr Paul drew the loudest cheers at Valley High School, as he laid out his contentious vision to end US military involvement overseas and take an axe to the federal budget to shrink the size of government. "We should not send young people off to war unless it is absolutely necessary," he said. The last ten years we have been fighting endless wars in the Middle East . . . and we're flat out broke.