Mr Romney, whom analysts on both sides of the political divide say will be a serious contender in 2008, was elected governor of Massachusetts — one of the bluest of Democrat blue states — as a social moderate. In the past year, however, he has changed his stance on social issues important to religious conservatives, the base of the Republican Party that wields enormous influence in the Republican primary race. Mr Romney once said that abortion should be “safe and legal”, but now opposes it. He denounced the decision by the Massachusetts Supreme Court to legalise gay marriage. Calling himself a “red speck in a blue state”, he has emphasised socially conservative positions on the death penalty, stem-cell research and birth control.

But Manuel Miranda, head of the Third Branch Conference, an alliance of conservative groups, said that many evangelicals view Mormonism — the Church of Jesus Christ of Latter-Day Saints — as a cult. Mr Miranda said that in 2000 he worked for Orrin Hatch, the Utah senator and a Mormon, during his unsuccessful bid for the Republican nomination. “Hatch had a poll done. He found that over 60 per cent of Americans would not vote for a Mormon.”

Richard Cizik, of the National Association of Evangelicals, said that Mormons were not Christians, and that profound doctrinal divisions would shape reactions to Mr Romney as a candidate for the White House. The view among evangelicals might change if Mr Romney’s main opponent is Rudy Giuliani, the former New York Mayor, who is socially moderate and supports abortion.

Frank Luntz, a Republican pollster, believes that Mr Romney’s religion will not be a significant issue. His biggest problem, Mr Luntz said, is that he comes from Massachusetts. Although he balanced the state’s budget, lowered taxes and improved education, “the last time Massachusetts produced a Republican candidate was never”.

Mr Romney may also face the charge of being a “flip-flopper” — an accusation that did so much damage to the last presidential candidate from Massachusetts with impossibly thick hair: John Kerry.

The last president to come from Massachusetts was John Kennedy, who successfully overcame concerns about being the first Roman Catholic in the White House.

Mr Romney can also take encouragement from the experience of his Mormon father, George Romney, who was Governor of Michigan. His 1968 presidential bid imploded after he said that he had been “brainwashed” into supporting the Vietnam War. “But until then,” Steve Hess, of the Brookings Institution, said, “there was no question he could have been elected.”