Leading Article: Yes. We. Can.

The certainty of Barack Obama's victory in the struggle for the Democratic Party nomination has been hardening for so many months that Hillary Clinton's formal concession was significant for its timing and tone rather than its content. For several months now, the Clinton campaign has been running on the basis that "anything can happen" – a basis made explicit by Mrs Clinton in unfortunate terms when she pointed out that Bobby Kennedy was assassinated in June of the 1968 primary season.

Even that, though, was not the real story. In reality, the Clinton campaign since March has been primarily one for the vice-presidential nomination. That campaign for second place has been, if anything, more forlorn than her attempt at the first prize. Mr Obama is no fool – that much, at least, has been established by this campaign – and was never likely to choose her as his running mate. Those demographic groups that her supporters claim she would bring to the ticket – the white working class, Hispanics and Roman Catholics – are mostly part of the Democratic base. They may have preferred her to Mr Obama in the primaries, but in the general election they are likely to rally to the Democratic candidate, whoever that may be. Besides, Mr Obama does not really want Bill Clinton as a third person on his ticket.

Thank you, then, Mrs Clinton, and goodnight. Yet her formal withdrawal from the race still marks a transition to a new level. However compelling the story of the primaries has been, this is now something bigger.

The general election starts with Barack Obama as the favourite, although his opinion-poll lead over John McCain, the Republican, is narrow – an average of three percentage points merely. Yet there is clearly something more enduring about Mr Obama's electoral appeal than the speaking style of a preacher, the timing of a stand-up comic and the articulate intelligence of a professor. In the highly personalised American system, his biography and character offer a leadership that makes possible the previously unthinkable.

In his book he tells the story of how a political consultant suggested that he would have to change his name after 9/11 if he were to have a future in politics, because of its similarity to Osama bin Laden. Indeed, he has been called Mr Osama, often by mistake in recent months, but it has not mattered.

As President, he offers to transcend divisions on the global stage. As Rupert Cornwell points out on page 32, by virtue of his ancestry and upbringing, he will transform the image of the United States in the world. As a man with an African father, brought up in a Muslim country, Indonesia, he would change American foreign relations simply by being in the White House.

This has huge implications for the infant doctrine of liberal interventionism, still in intensive care after the tragedy of Iraq. Looking back over this past week, we cannot afford to wave the doctrine away as a mistake of the Bush-Blair era. In Zimbabwe, Burma and Darfur, the world has an urgent obligation to give meaning to the new dictum of the United Nations, the "responsibility to protect". And in this debate Tony Blair was right about at least one thing: American power is crucial.

As we report today on page 10, in Zimbabwe, Robert Mugabe's campaign to retain power by intimidation and brutality continues unabated. Britain's role is constrained by Mugabe's use of our colonial history for propaganda purposes, but imagine for a moment the moral authority that could be brought to bear by a US President of part Kenyan descent. More than Mr McCain, Mr Obama offers the hope that we, the international community, can act together to set oppressed peoples free.

Mr Obama's willingness to engage in dialogue with leaders historically hostile to the US opens up the possibility that America's pre-eminent military strength might be used in future for humanitarian ends without provoking the kind of blow-back generated in Iraq and Afghanistan.

Both Mr McCain and Mr Obama would represent a welcome change in US leadership from George Bush. Indeed, the main reason Mr McCain secured his party's nomination was that he is as different from President Bush as it is possible to be and still be a Republican. On the issues that this newspaper cares about, Mr McCain has particular credibility on environmental policy. But when it comes to projecting US military power abroad, Mr McCain's policy would too easily be perceived as a continuation of that of Mr Bush.

American elections are the nearest that we have to a global democratic debate, and, already, Mr Obama has engaged people's sympathies outside America like never before. Not least for the sake of the people of Zimbabwe, we are drawn to the audacity of the hope he holds out.