Barack Obama has taken a giant step towards embodying the American dream as it has never been personified before. By securing enough additional delegates to be certain of the Democratic nomination for the United States presidential race, only John McCain, the oldest first-term presidential candidate in US history, stands in the way of Mr Obama becoming the first black man to enter the White House. First, there is the small matter to resolve of Hillary Clinton, who ran Mr Obama hard and close, though not close enough, for the Democratic nomination. It is surely only a matter of time before she concedes and takes her place in team Obama (the exact role is to be the subject of tough negotiation) against Mr McCain's Republicans.

Barack Obama has taken a giant step towards embodying the American dream as it has never been personified before. By securing enough additional delegates to be certain of the Democratic nomination for the United States presidential race, only John McCain, the oldest first-term presidential candidate in US history, stands in the way of Mr Obama becoming the first black man to enter the White House. First, there is the small matter to resolve of Hillary Clinton, who ran Mr Obama hard and close, though not close enough, for the Democratic nomination. It is surely only a matter of time before she concedes and takes her place in team Obama (the exact role is to be the subject of tough negotiation) against Mr McCain's Republicans.

Mr Obama has proved he is his party's best hope of winning power in the November general election. That a black man, from his background, should find himself leading the Democrats against a dispirited Republican party weighed down by a moribund President with embarrassingly low approval ratings is an achievement of note in itself. That he should be in this position after only four years as a senator verges on the astonishing. It is little wonder that Mr Obama says, with justifiable pride, that his story would not be possible in any other country on Earth.

When his parents married in 1960, a union such as theirs, between a white woman and a black man, was illegal in the majority of America's states. Only seven decades ago, the idea of a black President was so far-fetched that Gallup, the pollsters, did not ask people what they thought about it. For a time, his mother got by on food stamps.

For the Obama story to be completed, and for history truly to be made, the candidate must first beat Mr McCain. Winning the Democratic nomination is one thing. Winning the presidency is a different matter. The American electorate is whiter and more conservative than the Democratic Party. Is it ready for a black President? Mr Obama has youth, vigour and an easy, authoritative eloquence on his side. It was impossible to envisage George W Bush, despite eight years in the White House, making, far less understanding, the speech Mr Obama delivered to the American Israel Public Affairs Committee yesterday. He is a candidate of our times in terms of style and image. Voters have little to go on other than a sense of his personality, given his limited period in public life.

Just how much policy substance lies behind the persona, and what exactly is meant by change to believe in, will be the subject of scrutiny in the coming months. Mr Obama has shown a ruthless streak by ditching Jeremiah Wright, his inflammatory former pastor, and the preacher's church. In his time in the Senate he was prepared to take a cross-party approach on domestic issues.

In yesterday's speech, while demonstrating he could talk tough on Iran like Mr McCain, he emphasised his commitment to bipartisanship in the foreign affairs arena, too, with America once again engaging with the world. That is an enticing prospect compared with the crude reality of one of the worst two-term presidencies in American history.