Leading article: About-turn in Iraq

Is it "About-turn" in Iraq, or "As you were"? Both Gordon Brown and Barack Obama, the favourite to be the next president of the United States, claim to be preparing a more purposeful exit strategy. Yet, in neither case does the adjustment mark a sharp break with existing US-British policy. Mr Brown is generally assumed to have harboured doubts about the Iraq enterprise from the start, but has only ever been publicly supportive of the policy so identified with his predecessor.

His alleged doubts at the time are beside the point in any case; what matters now is his more obvious desire to distance himself from this part of the Bush-Blair legacy.

As our ComRes poll suggests today, he is in tune with public opinion. Two-thirds of voters say that Britain "should never have become involved in Iraq", and three-quarters want our troops "withdrawn from Iraq as soon as possible" – although the devil lies in the definition of "as soon as possible".

British forces should be pulled out of Iraq soon. As Raymond Whitaker reports today, their main activity now is training the Iraqi army. Their role as a back-up deterrent, the so-called "strategic reserve", proved unnecessary in the battle of Basra, which was fought in March this year by Iraqi troops with US mentors. Their only other role is as a symbol of British solidarity with the US presence in the north. That is not a trivial consideration, and it brings us to Mr Obama.

It is not clear to what extent Mr Brown and Mr Obama have co-ordinated their pronouncements in advance of this week's meeting in London. We suspect that this weekend's convergence has come about by two similar processes of triangulation. One is Mr Brown's triangulation between Mr Obama and John McCain, the Republican candidate, who supports the surge and refuses to put a time limit on America's commitment in Iraq. Mr Brown's policy was to cut troop numbers in Basra, a reduction that was postponed when trouble flared.

The other is Mr Obama's triangulation between his past opposition to the Iraq war, Mr McCain's greater credibility as a commander-in-chief and the Bush administration's unpopularity. The trade-offs involved have led to a blurring of edges as the world prepares for a possible Obama presidency. Through the haze, however, we can discern an alignment between Mr Obama's plan for US withdrawal within 16 months (a suspiciously precise target that is sure to be fudged) and Mr Brown's off-the-record suggestions that British troops could be out by mid-2010 (which also happens to be the most likely date for the next UK election).

If Mr Obama wins in November, therefore, it is possible there will be a rebalancing of the global polity for which this newspaper has argued since before the invasion of Iraq. For obvious reasons, the words of both Mr Obama and Mr Brown have been nebulous, but at last it is possible to make out the specifics of an exit strategy for US-British forces in Iraq.

And the reason this is so necessary is, as Mr Obama said in Kabul yesterday, that the international community should be focusing its military resources on Afghanistan. Although The Independent on Sunday led opposition to the Iraq war, we never regarded, as some of the anti-war movement do, Afghanistan as a morally equivalent abuse of American-led power. Contrary to that in Iraq, the cause in Afghanistan was just. One of our reasons for opposing the Iraq adventure was that it would divert attention and resources from the struggle worth fighting for, to bring freedom and security to the Afghan people. So it did, but now the international community has a chance to put that right.

Above all, that requires clarity about the mission in Afghanistan. As James Fergusson spelt out recently on these pages, we need "to scale down our ambitions there from what is desirable to something that might actually be achievable". The international force does not have and is not likely to have, even with redeployment from Iraq, the kinds of numbers to police the entire country. Even if it did have those kinds of resources, it would not be possible to "defeat" the Taliban militarily. We need to find our way more quickly to a political strategy of dividing the Taliban between its nationalist and al-Qa'ida wings.

That will still need a substantial military commitment in Afghanistan for years and possibly decades to come. And the precondition of that is a disengagement from the terrible mistake of Iraq. This weekend, we began to see how Britain could play a supporting role to a new US administration that was prepared to seek allies rather than expect them to follow. It involves reversing out of the dead end of Iraq, into which Bush and Blair led our two countries, and getting back on to the road to global solidarity that seemed briefly possible after 9/11.