Just a few months ago, President Obama was fruitlessly beseeching his Nato allies to show greater commitment to the Afghan mission. Now, it seems, his own commitment is wavering. It is easy to see why. The fraudulent re-election campaign of President Hamid Karzai has helped accentuate public and political resistance to the war in the US. But the President's wobble will lead many in the alliance to conclude that they are right not to pull their weight. It will also embolden the Taliban and its al-Qaeda allies, for the President's words will be taken across the region – rightly or wrongly – as a precursor to the scaling-back of America's commitment to the war. This is a potentially disastrous turn of events. Following on from last week's decision to scrap the missile defence shield in eastern Europe, it adds to the impression that Mr Obama is struggling to cope with the complexities of foreign affairs. This week he will address the UN General Assembly and chair a meeting of the Security Council. He must take the opportunity to clarify his war aims in Afghanistan – and dispel the dangerous confusion he has so carelessly created.