The potential risks and rewards
Says the UK Telegraph:

If the war is a great victory, if it lasts just a few days, and if it results in a democratic Iraq, Mr Bush will get a chance of being re-elected, Mr Blair will be vindicated, France will be cowed. A new Nato will probably rise from the ashes, centred on the "new" Europe: America, Britain, Spain, eastern Europe. The UN Security Council could lose its role as a body which blesses American interventions. The ability of European states such as Britain and Spain to make their own foreign policy, outside the European Union, will be strengthened.

But the war does not have to be lost to produce quite a different result. If it lasts much longer than it is supposed to do, if it degenerates into civil war, if the fighting in Baghdad is bloody and chaotic and expensive, then the aftermath may look quite different. President Bush may be finished, along with Mr Blair and Nato. France and Germany will once again be the most important countries in the EU. The next US president will think twice before doing anything without UN approval, and the next British prime minister will think twice before involving himself in foreign adventures without the explicit permission of his European colleagues.

There is an analogy with Suez here, although it is not precise. If the lesson of Suez was that Britain can't do anything without America, the lesson of a botched war in Iraq will be that a British prime minister can no longer make foreign policy outside the confines of the EU or act in defiance of Germany and France. The stakes are high here, much higher than the mere political futures of Mr Bush and Mr Blair. It is disturbing to think how much damage Saddam's Iraq, even in defeat, might still be able to wreak.