Most aspiring presidents and prime ministers face a myriad of challenges as they embark on their journey. Controversial issues, questions about ethics or past conduct, wounds within their party all raise their heads. But the doubts that Barack Obama faces are far more existential than the superficial questions about most candidates. They go to his very core as a person, calling into question his values, his world view, even his patriotism.

Hard racial divisions have softened in America, but fear of the “other” persists. Their possible next president has a strange name. He grew up in Hawaii and Indonesia. He had a Muslim Kenyan father who left when he was a baby. He made his political career in the cesspool of American politics - the traditionally corrupt Chicago Democratic machine.

His pastor of 20 years, after whose sermons he named a book, seems to hate white people in general and America in particular (despite $15 million federal funding for his church). His wife says that she is proud of America for the first time in her adult life - and she is in her mid-forties. He is a bit of a reach for the average American voter.

If he were white he would be suspect. But he comes from a world that few white voters know or understand. Fears linger that he is some kind of latter-day Manchurian candidate, a sleeper poised to take control of the US Government.

What makes all this particularly difficult to fathom is that Mr Obama is a mild-mannered intellectual, with a marvellous sense of poise and decorum, who handles himself eloquently and with dignity, bringing to politics a style and grace not seen since JFK. His pedigree includes Columbia University and Harvard Law, where he edited the Law Review. He taught constitutional law. His manner and appearance are as far from his controversial background and associates as one could imagine.

But the disjuncture between who he is and what his background and associations suggest he might be, is so profound that it leads to the most basic of doubts and worries among American voters.

Hillary Clinton has always been a bête noire to blue-collar, downscale, American men. But they lined up to vote for her, so deep was their fear of who Mr Obama might turn out to be. Their inveterate sexism was no match for the racial fears ignited by the questions around Mr Obama.

None of these questions is of Mr Obama's own making. In two years of campaigning, in an environment in which every waking moment is recorded, he has never uttered a single word to lend credence to those who imagine him an alien figure. He has been consistently classy, almost boringly straight. The worst one could say about him is that he is a Hamlet-like intellectual who is often subject to paralysis by analysis.

But to win, Mr Obama must reach down deep and dispel the doubts people have about him. So far, he has avoided inflaming them and taken great care not to lend them any credibility by his own statements or positions. Now, he must go further and reassure voters who want to believe him, but are afraid.

Is America ready for a black president? Hell, yes. Mr Obama's triumphs in states where there are virtually no blacks attest to it. Until the Rev Jeremiah Wright opened his mouth, the candidate was sweeping white voters. Even when the black community discovered Mr Obama and abandoned their historical affection for the Clintons, the white electorate refused to polarise along racial lines; Mr Obama consistently won about half of the white vote. But when Mr Wright spoke, he sent a shiver of fear down the nation's spine and millions of voters who wanted to back Mr Obama, and hated George W. Bush, abandoned the black candidate out of fear.

Blowing away this miasma of doubt will not be easy. Mr Obama, a private person who dislikes public displays of emotion, will have to speak from the heart about what America means to him. He will have to embrace our national sense of uniqueness and give voice to what Ronald Reagan said: “You can call it mysticism if you want to, but I have always believed that there was some divine plan that placed this great continent between two oceans to be sought out by those who were possessed of an abiding love of freedom and a special kind of courage.”

American exceptionalism is deeply rooted in our national consciousness and has been so offended by Mr Wright's characterisation of the US as a force of evil in the world that Mr Obama must assuage that hurt if he wishes to appease our fears.

While the US has always worked to keep Church separate from government, there has always been a kind of civil religion in America that speaks to our values and mission in the world. The president of the United States is the high priest of that religion and it is up to him to give it voice and apply it to the challenges that pop up in our path. Mr Obama must make clear to his countrymen that he subscribes to that faith and can pick up his duties as high priest. He needs to articulate the narrative that underpins the nation's faith in itself and show that he identifies with it.

I doubt that this election will be close. Either Mr Obama or John McCain will win it in a landslide, depending on whether or not Mr Obama can fulfil his existential mission of explaining to the American people who he really is.

Dick Morris was Bill Clinton's campaign manager in the 1996 election and encouraged him to pursue a policy of “triangulation”

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