The Prime Minister is right. The whole credibility of the United Nations is at stake this week. If the Security Council buckles under the US blackmail to which it is now subject over Iraq, we can discount the organisation as an independent force for international order.
Among Spectator readers there are still one or two of us who, prey to instincts we flatter ourselves to call Conservative, mistrust proposals for ruinous and dangerous military adventures. In a way we dare think consistent with remaining Tories, we doubt not America's goodwill but her judgment in world affairs. We find ourselves stumped for words at the cheating to which our Prime Minister and his new friends on the Right have stooped in their arguments for war. Nobody would call the hawk's mind open, but the door of his intellect does seem to have been hospitably open to a bewildering series of opposing arguments.
First we were told that the point of cleaving to Washington was to steer America away from unilateralism. Then Tony Blair announced that Britain's support was essentially unconditional.
We were told the UN inspectorate was in Iraq to find weapons (and shown pictures of jeeps racing from site to site) - then, when they found little, that the inspectorate had never been there to search. The Foreign Secretary said that if nothing was found, that proved it must be hidden. Lewis Carroll would have enjoyed that.
We were told invasion was to be justified as self-defence - then, when this failed to impress focus groups, that the motive was humanitarian.
We were told Saddam would never show his weapons - then, when he showed some, that this only proved he must be hiding more.
We were told Osama bin Laden was probably dead but al-Qa'eda remained linked to Baghdad - then, on the emergence of a bin Laden message which Washington pretended proved a link, that Osama was alive after all. The message made plain (as some of us always argued) that al-Qa'eda despised Saddam but hoped to muscle in on Muslim anger at America. Our government ignored the point.
We were told Colin Powell would present conclusive evidence of Iraqi non-compliance - then, when Mr Powell's presentation proved inconclusive, that proof was a needle in a haystack, and what should be sought was a change in Saddam's 'attitude'.
We were told the aim was to oust the whole Iraqi regime and that (as with Augusto Pinochet) there could be no haven for monsters; then that it would be 'great' (Tony Blair's word) if Saddam found a safe haven somewhere.
Finally we were told that, in international law, Resolution 1441 already justified an invasion - and then that a second resolution was, after all, to be sought - and then that if this was vetoed 'capriciously' (Mr Blair's word) the veto would not count.
How irrelevant, how silly and how shameless the debate is going to look in ten years' time. Life being short, we might do best to spend no further exasperated passion on the ebb and flow of this martial tide. The US President wants his war; the President usually gets his way. Maybe that is all there is to be said.
But my ears have pricked up twice in recent weeks. There might yet be something new to consider.
They pricked up first at an essay written by Andrew Tyrie. The Conservative MP for Chichester made a suggestion hitherto unvoiced in a debate which has taken American hegemony as a given. Many, including me, have implied that America will push the world around because America can.
But can she? asks Mr Tyrie. Let us have realpolitik by all means, but before we British cleave cynically to a superpower we judge unassailable, we should ask whether America does have the armies, the weaponry, the funds, the economic clout and the democratic staying power to carry all before her in the century ahead. How many wars on how many fronts could she sustain at once? How much fighting can she fund? How much does she need to export? Is she really unchallenged by any other economic bloc? Even the biggest boy in the playground can be thwarted by gangs. If Blair's instinct is to back a bully, he had better be sure this one is big and strong enough to reward his loyalty. Are we backing a long-term winner?
My second new thought is related. My ears pricked up at Mr Blair's suggestion that the standing or falling of a Security Council resolution may not be a simple jurisprudential fact, but less or more valid depending on whether a Permanent Member has acted capriciously.
Blair's choice of 'caprice' as capable of invalidating a veto is, of course, absurd and insulting. Even those who disagreed with France (for instance) would accept that she could cast her veto in serious good faith. More familiar to jurisprudence than the concept of caprice, however, is that of duress. Duress certainly can invalidate a decision-making process. And there is a powerful argument that a Security Council endorsement for war can now be obtained only under duress. What else can explain all the bribing, blackmailing and arm-twisting this week as emissaries from London and Washington toured the globe in search of Security Council members susceptible to being heavied?
Whatever the strength in law of my argument, there can be no doubt of its strength in the world's perception of events. Nobody is seriously going to conclude that there was ever any possibility that the United Nations would authorise war this month on its own independent judgment. History will record that they were bullied into compliance.
How Tony Blair or George W. Bush can have argued that by complying now the UN will escape 'irrelevance' escapes me. 'Do what I say or you'll be irrelevant' rather suggests that this is already how you are seen. All week the Security Council has been made a mockery of by Washington. Compliance with America now would invite the judgment that the organisation was bent to Washington's will. What legitimacy is lent a decision by forcing a third party to rubber-stamp it? Few British voters, and perhaps fewer Labour backbenchers than Mr Blair thinks, will be impressed by this. To comply with Washington will break the UN's back.
But (you ask) what is the UN's alternative? To be pushed aside by America? That is indeed the alternative and I recommend it. Pushed aside, perhaps, but enhanced in self-respect.
I see - and, watching him in Algeria, I think the President of France may see - a new arrangement emerging among nations. A potentially large and inevitably loose-knit network of sovereign states who do not take Washington's whip may be swimming into shape.
Diplomatic leadership in this unaligned world will be important, and Britain would have been well placed to share it. I am sorry that, at what may be a critical moment, our Prime Minister has proved blind to the opportunity. To seize it would in the real sense have been bold.
Matthew Parris is a political columnist of the Times.