Mega-rich, Mormon, chilly and ruthless – Mitt Romney may emerge as the Republicans' candidate to take on Barack Obama, but he has a good few obstacles to get over first

'Well, it's just great to be here!" Mitt Romney says as he bounds on to the stage at a campaign stop in January, just one of hundreds he has made in his epic journey – he hopes – to the White House. It is the first of three rallies he will be packing into a single day, this one held in the open air at a small liberal arts college in Spartanburg, South Carolina.

"This is gorgeous, absolutely gorgeous," he continues, a perma-grin glued to his face. He has a way of talking down to the crowd, pausing after every sentence to allow them to soak it up, that is disconcertingly suggestive of that old pantomime favourite, Widow Twankey. "What kind of tree is that?" he says, looking up at the branches that arch over him with an expression of mock surprise. "I don't even know. Is it a Mitt Romney tree?"

The crowd laughs heartily, which is peculiar given the quality of the "joke" and the fact that, unlike a pantomime, there are few three-year-olds in the audience. (Besides, as any motley fool could tell you, the tree under which he is speaking is a laurel oak, Quercus hemisphaerica.)

It has been a rum old fortnight for the former governor of Massachusetts. Since 2007 he has been on the campaign trail virtually without pause, laying down a nationwide network of volunteers, fundraisers and supporters that his rivals – Newt Gingrich, Rick Santorum and Ron Paul – can only dream of. In the tradition of American politics, where money and political influence do the talking, the Republican nomination rightfully belongs to him. Yet it is proving heavy going. Core Republican voters continue to distrust him, turning restlessly to a succession of alternatives. They have toyed with Rick Perry, Herman Cain, Ron Paul, Rick Santorum and Newt Gingrich – the current bearer of the Not-Mitt-Romney mantle.

As the polls open on Tuesday in the potentially decisive primary vote in Florida, Romney remains the putative frontrunner. Most pundits believe he will weather the storm – Hurricane Newt, you might call it – and go on to face Barack Obama in the presidential election on 6 November. But after all the battering he has taken this month, you have to wonder. Why do his own people seem to dislike him so much? And who is this man who could become leader of the most powerful nation on earth, anyway?

Romney's campaigning style is not as dire as it was four years ago, when he had all the panache of a donkey. This time round, his stump speech is still scripted to death, to the extent that once you have heard him deliver it a few times you can mouth along to it like a pop song. But he is loosened up, discarding tie and suit for jeans and gingham and with his wife, Ann, on his arm. Nonetheless, a nagging disconnect remains. As a Boston business acquaintance puts it in Ronald Scott's biography of Romney: "There's no heart, like the Tin Man."

Even those who know Romney well, such as Bob Bennett, US senator for Utah until last year, agree he can come across as rather detached. Bennett says that Romney's true passion is for problem solving and number crunching, skills he picked up at Harvard Business School and developed as a management consultant at Bain & Co.

"Mitt loves to wallow in the data," Bennett says. "His first instinct is to say: 'Show me the data, let's work out the problem.' It's an accountant's mentality – he doesn't have the habit of raising his head and giving a smile to a passer-by."

Bennett and Romney are life-long members of the Church of Jesus Christ of Latter-day Saints: Mormons to you and me. When Romney ran for his party's presidential nomination in 2008, his religion was a big sticking point for Republican voters, particularly evangelical Christians. Bennett campaigned for him in Iowa in 2008 and recalls being stunned by the degree of anti-Mormon feeling. "Wow! Mormons are a Satanic cult dedicated to the overthrow of the United States!"

Four years on, anti-Mormon sentiment continues to run beneath the surface, particularly among evangelical Christians who see Mormonism as a cult. Such antagonisms help explain the difficulty Romney has had in wooing Republican voters in states such as Iowa and South Carolina where the Christian right is prevalent, and it could be a subliminal problem for him should he go on to face Obama. But overt anti-Mormon prejudice is now much less prevalent a sea-change that Bennett puts down to it being yesterday's news. That is not to say that Mormonism has become irrelevant to Romney, the man or candidate. It remains a central part of who he is, from his five Mormon boys and 16 Mormon grandchildren to the core of his 64-year-old character.

He was brought up in the faith in Michigan, where his father was governor, and spent a formative two years in France as a missionary, returning to study at the Mormon Brigham Young university in Utah. When he later settled in Boston, he became a prominent church leader, first as a bishop of a local ward and then as overseer of a group of wards, a role known as "stake president". That had a personal significance unique to Mormonism. "The Mormon church doesn't have a professional clergy, everything is done by the members," Bennett says. "Romney would have had to deal with all kinds of situations: personal problems, marital problems, financial problems, teenagers going wild." The experience, Bennett suggests, would have instilled in him initiative, decisiveness, willingness to take risks, and crucially empathy for those less well off.

Empathy? Romney? Really?

"I know that doesn't come across in his public person, but empathy is central to his experience," Bennett says. But doesn't that conflict with Mitt Romney, the data wonk who once notably said: "There is gold in numbers"? "You have a tug of war in his personality – the part strengthened by his church service that is extremely empathetic, and the part that is extremely analytical that turns people off."

Before I let Bennett go, I have to put to him the question about Romney that everyone wants to ask but few have the guts to do so. Of course he wears Mormon underpants every day, Bennett replies – they are a symbol of the covenants each member takes inside the temple. And that may have more significance to the 2012 presidential race than you might think.

"If you are going to violate those vows – let's say by being unfaithful to your wife – you have to take the undergarments off first, and that makes it more difficult," Bennett says. In an election year that has featured alleged sexual harassment by Cain and Gingrich's open marriage proposal, Romney's Mormon underpants might just be the secret weapon that clinches him the nomination.

Romney first ran for political office in 1994, when he tried to wrestle the Massachusetts senate seat from Teddy Kennedy. He lost, unsurprisingly, having been pummelled by Democratic attack ads that focused on two perceived weaknesses – his tendency to flip flop on policies, and his ruthlessness as a businessman. Remarkably, 18 years later exactly the same two accusations continue to dog the candidate. The only difference this time is that the cries of flip-flopper and evil entrepreneur have come from rivals within his own party and from the diametrically opposed direction.

Take abortion. As a Mormon, Romney's default setting is anti-abortion. Yet when he faced Kennedy in socially liberal Massachusetts, he did a 180º turn, dredging up the story of a "close relative" who died in the 60s from an illegal operation, which taught him, he said, never to impose his beliefs on others. Eighteen years later, he has made another 180º turn, and is now full circle back to the anti-abortion position. As Kennedy put it deftly back in 1994: "I'm pro-choice; my opponent is multiple-choice."

Romney has shown impressive pliability too on healthcare. The groundbreaking law that he signed as governor of Massachusetts in 2006 providing health insurance for all – "Romneycare" as Gingrich and Santorum stingingly call it – provided the model for Obama's federal reforms. Romney insists he is proud of his health reforms, yet he promises at every campaign stop to repeal "Obamacare" as one of his first acts in the White House.

Those inconsistencies are problematic, but they have so far been overshadowed by the second of his perceived weaknesses – his business record coupled with his vast personal wealth. Gingrich won South Carolina on 21 January and put the Romney campaign momentarily on the skids largely by calling into question his brand of capitalism and portraying him as an out-of-touch rich kid. Along the way, Romney has had to defend himself against the charge that he was a "vulture capitalist" (Perry's memorable phrase) and been forced to reveal that he paid less than 14% tax on his 2010 income of more than $20m, and that he has millions of dollars squirrelled away in the Cayman Islands and a closed bank account in Switzerland.

That hasn't looked good, on any level, says political analyst Larry Sabato. "To run for the presidency for five years yet leave money in the Caymans and a Swiss bank account – this is a classic case of a candidate avoiding facing up to a difficult issue."

Then there's Bain Capital, the private equity firm that Romney set up in the 80s through which he amassed most of his fortune of up to $250m. Bain Capital has haunted Romney in the pursuit of his political ambitions ever since that Kennedy election, as Randy Johnson can testify.

Two months before the 1994 ballot, Johnson and fellow workers at a manufacturing plant in Indiana went on strike. The factory was owned by a company called Ampad that had recently been taken over by Bain Capital. The strike, organised by a local union branch headed by Johnson, was in protest at the way Bain Capital had arranged for all the workers to be sacked and then rehired on much worse conditions – less pay, longer hours, no work pension. When the election got underway, Kennedy contacted Johnson and brought him to Boston to publicise the brutal way the workers had been treated at the hands of Romney.

Today, Johnson is again travelling the country, funded by the Democratic party, repeating his cautionary tale about Romney's way of doing business. The Ampad factory was closed in February 1995 and Johnson and many others lost their jobs. Ampad itself was loaded with so much debt, including huge fees exacted by Bain Capital, that it went into bankruptcy in 2000 while Bain Capital walked away with $102m in profits.

"What happened to me is a part of Romney's history he can't escape," Johnson says. "He talks about living the American dream by running for president, but what about the folk whose American dream – just to make it through to retirement – he shattered?"

Howard Anderson has a very different perspective on Bain Capital. He used to work as a venture capitalist himself and entered into several joint deals with Romney in the 80s. Now a lecturer at MIT, Anderson does not see the candidate as a vulture capitalist – it was never the intention to sack people and drive factories into the ground, though in some cases that happened. But Anderson shares Johnson's take on the candidate in this regard: that Romney's oft-repeated claim that he is equipped to be a job-creating president because of his record as a job creator at Bain is hokum. "He was never about creating jobs. He was about creating wealth. That was his only mission, and he would do whatever it takes."

Until a few years ago, Romney had a phrase for it: "creative destruction". If you judge creativity by the balance sheet, as Romney the number cruncher did, it certainly worked. Between setting up Bain Capital in 1984 and quitting to run the Winter Olympics in 1999, Romney led the firm to a staggering 88% annual rate of return.

You won't hear Romney utter "creative destruction" in his stump spiel these days. Instead, he refers to himself as a "turnaround guy" who saved the Winter Olympics and eradicated Massachusetts' $3bn budget shortfall, who will now do the same on a bigger scale for the US. He says he wants to restore the country to the kind of capitalism that existed before Obama began destroying it – a society based on merit and opportunity, where one person's success (implicitly his own) is to the benefit of everybody else.

"People want real change that will take us back to the strength America had in the past," Romney tells the crowd at the third and last campaign stop of the day. "This election comes down to a clear choice, with two very distinct paths: on the one hand we can go down the path of President Obama, who takes his inspiration from the social democracies of Europe. I take my inspiration from the towns and cities of America."

Which brings us to the biggest question of all about Romney. It is a fair bet that over the next month or two he will slug his way to the Republican nomination, overcoming Gingrich through sheer – as befits a data wonk – force of numbers. So what kind of adversary will he be when he goes up against Obama come the presidential election proper?

The first point to make is that he should not be underestimated. He may come across as Widow Twankey on the campaign stump, but he fights hard and he fights dirty. He has neutralised much of the Gingrich threat through a blitzkrieg of negative TV advertising that was impressive even by America's sullied standards. In Florida alone he has spent almost $14m (£9m) on attack ads, $8m (£5m) of that through Restore Our Future, a Super Pac, or political action committee, that Romney pretends he has nothing to do with but is run by his former advisers. Over the past 10 days he has eviscerated Gingrich, depicting him as a lobbyist for the much-hated mortgage giant Freddie Mac and virtually accusing him of lying about his close relationship to Ronald Reagan. The assault was surgical, brutal and chillingly effective. And all the while, Romney kept that perma-smile glued to his face.

Expect similar treatment of Obama, who Romney will portray, as he does on the campaign stump, as a European-style socialist destroying free enterprise and the God-given right to pursue happiness that is the cornerstone of American greatness. It is a Tea Party argument that Romney, ever the chameleon, has adopted and made his own. Though he is likely to soften the message a little in order for it to reach beyond the Republican faithful he is appealing to now, the idea that Obama is somehow un-American is likely to suffuse the attack ads that will be unleashed from the summer with an intensity unparalleled in US history.

There is some brighter news for Obama in all this. Romney has undoubtedly emerged bloodied from the beating of the past few days. In no small measure, Gingrich, Perry and the rest of the Republican mob have done Obama's preparatory work for him. "People have learned lots of disturbing facts about Romney over the past couple of weeks that will hurt him in the presidential election, and it's all come from Republicans," Sabato says. "All Obama needs to do is splice Perry calling him a vulture capitalist together with Gingrich on the Cayman Islands, and Romney has a problem."