Leading article: A morning of hope and goodwill in America

The long transition between an American election and the inauguration means that the actual import of the occasion can all too easily be taken for granted. Not this year. The excitement that has been mounting in Washington since the night of 4 November has radiated not only across the United States, but around the world.

At midday today, east coast time, power in the country that is still the world's richest and mightiest will be transferred, as the constitution decrees, to Barack Obama. Thanks to satellite television, it will be one of the most watched events ever – a truly global occasion, and a model of how democracy should work.

At 47, Mr Obama will not be the youngest President of the United States. But that is one of the few barriers he has not shattered on his triumphant progress to the White House. As the outsider, contesting the Democratic Party's nomination against Hillary Clinton, one of the best connected and best funded candidates on record, he ran an inspirational grassroots campaign. With his rhetorical gifts and his unique personal history, he mobilised young Americans and those of all ethnic backgrounds – some of the voters always hardest to reach. Imaginative use of the internet spread the word and brought in the money; he raised more and spent more than his rival.

Still the underdog at the start of the election campaign proper, Mr Obama overtook an increasingly elderly-looking, but still appealing opponent in John McCain. Had the focus remained on national security, rather than on the gathering economic storm, the contest might have been more equal. As it was, Mr Obama out-campaigned and outclassed the old warrior, with his mastery of detail, his energy and his can-do optimism.

An America that had been sharply divided along ideological lines through the Clinton years, and then again as a result of George Bush's disputed victory of 2000, elected Barack Obama by a landslide. As the first black – strictly speaking, mixed race – man to be elected to the highest office in the land, he has broken what could be regarded as America's last taboo, almost a century and a half after Abraham Lincoln abolished slavery. That this was even conceivable, let alone possible, says a great deal about Mr Obama, but just as much about what is most admirable in the United States.

Mr Obama assumes the US Presidency at a time of complexity and risk perhaps without precedent in recent times. The hopes he has raised, at home and around the world, may be unrealistic; some are bound to be frustrated. But a surfeit of hope is surely better than excessive trepidation. This is Barack Obama's day; the harsh realities will crowd in tomorrow.