In an almost unprecedented move the US Congress passed legislation on Thursday requiring the President to begin withdrawing troops from Iraq.

Whether or not he vetoes the Bill, it is now official: a handful of chisel-jawed insurgents in sandals armed with little more than Kalashnikovs and crude explosive devices has broken the will of America to fight and win a war. For the first time in history a guerilla army has militarily defeated a superpower without the backing of any power more super than Iran.

The interesting thing about the Iraq war is that it could turn out to be the war America won by losing it.

General Sir Rupert Smith always teaches his student officers at Sandhurst never to send out a force they can’t get back. Success in war is about creating a condition advantageous to yourself that can sustain itself even after your forces have gone home.

A US pull-out next year would not necessarily put straight tens on the insurgents’ scorecard. American military commanders reported in mid-April that at least two Sunni insurgent groups have been putting al Qaeda on the wrong end of a shark feast. Repelled by their sheer brutality and austere religious extremism a growing number of tribes have decided to impose a final solution the old-fashioned Arab way. For al Qaeda, then, nul points.

The Americans have scored remarkably highly for a defeated nation. For overthrowing Saddam Hussein and bringing him to justice, and making sure there were no WMDs in the country douze points. For luring al Qaeda to a Mesopotamian extermination, again douze points.

For giving Kurdistan a reasonable measure of security and stability, I think I’ll give them dix points.

But for basing the legality of the war on shaky arguments about WMD when there were better arguments to be had, I’m afraid it has to be deux points for Bush and nul points for Blair. As a lawyer and the spouse of a judge Blair had no excuse. He and his wife between them could have drawn on a wealth of jurisprudence from the International Criminal Tribunals for Rwanda and Yugoslavia to demonstrate that the obligation to punish genocide - of which Saddam Hussein was guilty in spades - is of such vital interest that it overrides even the prohibition on the use of force enshrined in the UN Charter. In other words you don’t need a Security Council Resolution to have gone after him, though the Council issued plenty of them after the event.

Whether America will win the war despite losing it depends on whether, when the dust settles, Iraq ends up with a government as hostile as that of Iran or as friendly as that of Jordan. This is one of Rumsfelds "known unknowns" you can’t see for the fog of war. Tous les points are up for grabs. There are two possible futures for Iraq.

The first is that the Arabs decide to dive into a welter of blood and fire, unwilling to summon the character to fight for democracy and uphold it.  In that case even I will be convinced that democracy simply is not for them. The only question that will then need to exercise the Americans is whether or not the resulting strongman is their sonofabitch, and if he isn’t then how much can he be bought for.

The second future is that, against all the odds, the Iraqis actually emerge victorious over the insurgents and make democracy work. And then they can tell their children to always cherish it and never forget the hundreds of thousands who died as the price of it.