Downing Street is at panic stations as the full implications of Hans Blix's inspections report sink in. The two main US-British arguments in favour of launching a war on Iraq next month - that Saddam currently possesses deployable weapons of mass destruction and poses an immediate or near-term threat to the region and to us - already had few takers before Friday's UN meeting. In his peculiarly dispassionate, persuasive way, Blix further undermined and, for many, destroyed the credibility of the Anglo-American case for an early, pre-emptive attack.
A third core argument, favoured by George Bush and blithely reiterated by him in Florida last week - that Saddam is in cahoots with al-Qaida and is somehow linked or even to blame for 9/11 - is not seen as convincing even by those who have espoused it. Downing Street now knows this argument, too, is a definitive non-runner.
Assailed on all sides by unprecedented popular protest, at odds with Europe, outnumbered in the security council, with the Pentagon's clock inexorably ticking, and rightly worried that an impatient Bush may reject the "UN route", dish his British ally and press on regardless, Tony Blair has now reached his bottom line: morality.
With his back against the wall, belatedly aware of the depth of his difficulty, and surrounded by the empty shell casings of a defeated polemic, Blair played his last card in Glasgow at the weekend. Action was a moral imperative, he declared. If Saddam remains in power, he warned emotively, there will be "consequences paid in blood". The moral case for intervention was overwhelming. Those who opposed it, he implied, were themselves acting immorally.