Every American child learns at a parent’s knee the most fundamental of truths about their country. Anyone can grow up to be president of the United States. It is the essence of the nation’s republican ideal, the meritocratic belief at the core of its organising principle. It is also, at least empirically speaking, complete balderdash.

In 220 years a country that has steadily multiplied in diversity, where ethnic minorities and women have risen to the very highest positions in so many fields of human life, has chosen a succession of 42 white men as its leader. For good measure, the vice-presidency, the only other nationally directly elected position in the US government, has been held by a succession of 46 white males

But last night, in a tumultuous break with this long history, the ultimate realisation of the American dream moved a little closer, and a black man became his party’s nominee for the presidency.

The fact that Barack Obama has been headed for the Democratic nomination has been obvious for months. But that did not make the final moment of arithmetical certainty any less dramatic or historic.

It will not be lost on ironists that Senator Obama finally broke the barrier by crushing the hopes of the most plausible woman candidate for the presidency in the country’s history. But neither should the significance of this landmark be missed.

Despite the unexpectedly long Democratic primary, there will be plenty of time for Americans to scrutinise Mr Obama and probe his flaws: his inexperience, his solidly left-of-centre politics, his somewhat questionable friends, allies and mentors. But for the moment it is surely time simply to acknowledge his remarkable political achievement.

Six months ago he was given almost no hope. He was taking on the establishment, the First Family of Democratic politics. Barely three years into the Senate, his bid was seen as audacious, even a little disrespectful. It’s hard to recall now, but back then it didn’t even seem likely that he would win a majority of black voters. They were wedded to the Clintons politically and wondered aloud whether Mr Obama, a second-generation, mixed-race African-American, was “black enough” to understand and articulate their frustrations and hopes.

So it is a testament to his extraordinary political skills, his stirring oratory and, above all, the change represented by his eloquent calls for an end to partisanship, his relative youth and, yes, his skin colour. He brilliantly channelled opposition to the war in Iraq — having been one of the few Democrats courageous enough to oppose it in the first place — and ended up winning not only almost the entire black Democratic vote, but breaking the colour bar and gaining enough — just — of the white vote to win the nomination.

A word of caution is in order on this historic day. Mr Obama will be well aware that the pioneers of ethnic, religious or gender presidential equality rarely make it all the way to the White House. The first Roman Catholic to win a party’s nomination was Al Smith in 1928. But no Catholic was elected president until John F. Kennedy 32 years later. The first woman to appear on a presidential ticket was Geraldine Ferraro for vice-president in 1984. But 24 years later, as Hillary Clinton would acidly note, no woman has been elected president. The first Jewish candidate was vice-presidential nominee Joseph Lieberman in 2000. But he lost, too.

So it’s fair to wonder, as the 2008 US general election finally gets under way, whether this might be just another false start.

It might. But for the time being, Barack Obama is changing the world.

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