Leading article: The horror story that is unfolding before us

The midterm elections have left America's policy on Iraq in a state of confusion. The Defence Secretary, Donald Rumsfeld, has been sacked, and President Bush seems to have outsourced strategic thinking on the subject to James Baker's Iraq Survey Group, which is not expected to report until next year. The newly resurgent Democrats will have a profound influence on what happens now, too. They must decide whether to pursue a bipartisan approach to Iraq or increase the pressure on the Republican administration in preparation for the 2008 presidential elections. But if Washington's senators, congressmen and policymakers have any sense of responsibility they will divert their attention from matters of domestic advantage, and concentrate on the interests of the Iraqi people.

To grapple with this question it is necessary to recognise the scale of the horror facing Iraq. The prospect of the break-up of the country into separate Shia, Sunni and Kurdish blocks looks increasingly unavoidable. The national government of Nouri al-Maliki is weak and lacks popular legitimacy. Ethnic cleansing on the ground is well advanced. American and British troops are doing nothing to prevent this. Nor is our military presence stopping the sectarian killing. As for the Iraqi national police force and army, they seem too feeble or compromised by the infiltration of sectarian militias to perform their security duties. The north of the country is relatively peaceful, but this is because the Kurds are well on their way to autonomy already.

But history shows that the abrupt withdrawal of foreign forces in collapsing states generally intensifies the slaughter. The spectre of the partition of India still looms large. It is chilling to think what could happen in Baghdad, which has broken up into several separate sectarian enclaves. It is also impossible to divide up Iraq's oil wealth in a way that would suit the various groups. The Sunnis would most likely be left with nothing.

This is a recipe for a lengthy civil war, and a no-win situation for the US and Britain. If our troops remain, we will see the country crumble gradually and more British and American soldiers die at the hands of an increasingly sophisticated insurgency. If our troops go, they will leave Iraq to cataclysm, tarnishing the reputation of the US and the UK abroad still further. Yesterday, the Foreign Secretary, Margaret Beckett, warned us that leaving would create "a very real risk of even greater instability and bloodshed than we've already seen". Quite so. But Ms Beckett and all those politicians on both sides of the Atlantic who supported this invasion should acknowledge their responsibility for the terrible choice now facing us.

Some are recommending a third option. Mr Baker, a former secretary of state, has hinted that his report may recommend an appeal to neighbouring Iran to help stabilise the Shia south of the country. He has also suggested that Syria be requested to influence Iraq's Sunni population. This seems the most pragmatic course on offer.

But even this is by no means guaranteed to succeed. The Shia are fighting among themselves, with the Iranian-sponsored Badr Brigade vying for dominance with the followers of the cleric Muqtada al-Sadr. Iran may find that its influence in the south is limited. On the other hand, Syria and Iran may decide they would like a share of Iraq's oil wealth for themselves, leading to a bloody regional struggle. There would be little the US, or Britain, could do in such a scenario.

The dreadful truth is that, no matter what strategy our leaders now settle upon, the fate of Iraq is slipping inexorably out of their hands.