Obama talked the talk: now he owns problem of two wars

It pushed through an unwilling international community to a war with an aftermath it had not properly planned and which it could not control -with immense loss of life in its own ranks, among its allies and in the population it had come to liberate from Saddam Hussein.

Mr Obama is president-elect for a number of reasons today, but Iraq looms very large among them. Unconditional opposition to the invasion gave him a defining platform against the more nuanced view of Hillary Clinton, and connected him with widespread anger about the conduct of the war.

Now, as Colin Powell once warned President Bush in vain, he is the man who "owns the problem". He must therefore shift his focus from the "wrong war at the wrong time" rhetoric which won him votes in the campaign, to a more detailed and plausible account of how he intends to draw down US troops.

Barely anyone involved in Iraq policy planning believes that Mr Obama's stated aspiration to bring the troops home in 16 months can be achieved without exacerbating the violence in Iraq and wasting the gains of the troop surge.

General David Petraeus, who masterminded the surge, has been promoted and will oversee both Iraq and Afghanistan operations. He is highly unlikely to endorse a cut and run that could worsen events on the ground simply to fulfil an implied campaign promise.

So President Obama will aim to show that the draw-down of troops is heading in the right direction: so long as he can get the last American forces home by the time he runs for a second term.

Despite conveying the impression on the campaign trail that a vote for him would mean swift disengagement, he will have more room for a manoeuvre than his predecessor, who had come to be negatively defined by his Iraq strategy.

Not that Mr Obama will be short of other major headaches. Afghanistan has taken over from Iraq as the major US and British engagement, already exacting a heavy casualty and death toll, causing rows in the coalition about the limited results and unclear strategy.

But Americans - even many who opposed the Iraq war - remember that 9/11 was possible because Osama bin Laden had been able to use Afghanistan as a recruiting and training ground for terrorism.

That has been complicated by the deterioration in security in neighbouring Pakistan and especially the border areas. "Increasingly, we are going to have to regard this as one theatre of operation, diplomatically and militarily," says one senior British diplomatic source.

The internal politics and tribal divides of Afghanistan have bogged down the US and UK mission there, with a dawning realisation that the outside world has little real leverage over Afghan power politics. One of the early decisions Mr Obama will have to make is how far he follows President Bush in supporting President Karzai.

Privately, diplomatic sources speak of their concern that Mr Karzai has not proved strong enough and allowed the security situation in Kabul to decline to a dangerous point. But there is no guarantee a replacement would improve the record - or drive ahead vital cooperation with Pakistan.

An unfair charge levelled at Mr Bush in his final months was that he was hyping up concern over Iran's nuclear programme and that his discussion of a military option was just another example of his trigger-happy ways.

But alarm is growing in Washington about Tehran's pursuit of the bomb. Mr Obama hardened his tone in the past fortnight, as have many others in foreign policy circles.

One Obama adviser says that a military strike on Iran's nuclear facility would be "a terrible choice," but adds: "Sometimes in a terrible world we might have to get to grips with such a choice."

Still, there will be some welcome differences for European governments dealing with the US. Mr Obama has made clear that he wishes to re-engage America diplomatically and he is likely to attempt to come to a more cordial relationship with the UN after President Bush's contempt.

Economically, the president-elect will have to reconcile some protectionist instincts, fuelled by the rise of China, with the need for America to play a key part in the world economy at a crucial time.

He will almost certainly try to establish early entente with Prime Minister Vladimir Putin. After the Georgia debacle this summer, Nato expansion is a dead duck. "He might as well trade it away for some Russian co-operation," says a UN leading diplomat.

More troublesome is the future of the missile defence shield, which has angered the Russians by being sited in eastern Europe.

A growing body of opinion says that this project - the offspring of Ronald Reagan's "star wars", is more geo-political trouble than it is worth. Mr Obama may therefore consider abandoning it in return for Moscow's guarantees of better behaviour towards its neighbours, improved human rights and cooperation on energy and Iran.

One of Mr Obama's strengths is the perception that he could free America from the unwelcome burdens of engagement. But the US cannot afford to retreat into its shell at a time of turmoil and with power play more complex than it has been at any time since the Cold War ended. Mr Obama now owns rather a lot of problems around the world and their outcome affects us all.