Rupert Cornwell: Cool guy, Barack. But could he be too cool for US voters?

The Democrat candidate can come across as cerebral and fastidious, even supercilious

We still have three months to go before Americans cast a vote in one of the most important Presidential elections of the modern era. But a gnawing unease assails Democrats across the land. Why isn't Barack doing better?

Everything, after all, is running their way. Polls show Democrats with a double digit lead over Republicans in terms of basic support. It would be astonishing if Obama's party did not make big gains in both the Senate and House this autumn, in the congressional elections on the presidential undercard.

If ever circumstances were propitious to a Democratic White House landslide, it is this year: huge economic insecurity, an unpopular war and an even more unpopular president, coupled with a philosophical shift away from the "markets know best", deregulatory approach, that marked the Republican era now approaching its end. Big government is back in fashion.

The candidate, moreover, is fresh from a foreign tour that banished many doubts about Obama's command of foreign policy. He made no gaffes – indeed his Iraq withdrawal strategy was endorsed by prime minister Maliki himself. Passing a crucial test, he looked and spoke like a president. And yet, despite everything, he leads John McCain in the polls by a whisker, if at all. Key swing states – Ohio, Michigan, Pennsylvania, Florida, for instance – are a toss-up.

And it's not as if McCain has been playing a blinder. Yes, he's run a couple of effective ads, one portraying Obama as a vacuous celebrity like Britney Spears and Paris Hilton, the other a web-only production that mocks Obama as "The One" (as in messiah). McCain has also extracted more political mileage, so to speak, from soaring petrol prices. But he remains a listless speaker, who sets no audiences on fire. More than once, he's made slips that have you wondering about his greatest weakness, his age.

So what is happening? A clue to the answer came last week. Obama was on Capitol Hill, at a closed meeting with senior Democrats in the House. He told them, according to accounts afterwards, that the success of his trip had proved he was the US leader that a world yearning to re-embrace America was waiting for.

That's probably true. But such sentiments do not go down well out in the heartland of his own country – not, for instance, among the tens of thousands of Harley-Davidson devotees gathered for the annual bikers' jamboree in Sturgis, South Dakota, whom McCain went courting on Monday evening.

At one level, the competing images tap into that hoary old dictum about US presidential elections (one no less true for being hoary) that, all other things being equal, Americans tend to vote for the "regular guy", the candidate they'd rather have a beer or a coffee with. Measured by this standard, McCain versus Obama is currently no contest. For all his recent conversion to Republican orthodoxy, in the public mind the Arizona senator is still the congenial maverick, gossipy and indiscreet, ruled by his heart, not his head.

For that reason too, the press still love him, even as it wearies of its once unquestioning love affair with Obama, complaining about the latter's hyper-controlling campaign staff, and the lack of access to the candidate. Much the same goes for the legions of poorer white Democrats who once voted for Hillary and still can't come to terms with the man who defeated her.

Obama is cool, maybe too cool. To the public as well as the media, he can come across as cerebral and fastidious, even supercilious. As candidates must, he braves pancake houses and diners. But he visibly disdains fast food – and in a land where obesity is king there is, according to his doctor, not an ounce of excess body fat on his body. "Too fit to be President?" ran the Wall Street Journal headline. The question was by no means facetious. However famous his face, however much has been written about him, Obama remains largely a mystery. His life narrative is simply too exotic, too far from the mainstream.

However, if presidential campaigns seem to go on for ever, their very length has the redeeming virtue of allowing such unfamiliarity to be removed. That is why these final three months of the campaign are so important for Obama.

But Democrats shouldn't worry too much. This is a watershed election, akin to 1932 which ushered in a Democratic era, and 1980, when Ronald Reagan's victory opened the conservative era that is now ending. On that occasion, Reagan and Carter were neck and neck until late in the day. Finally, though, the country decided it could trust Reagan, and a Republican landslide followed. The same can happen this time for the Democrats – and Obama.