The crucial question remains: is the Iraqi President mad as well as bad?

Even if Saddam had nuclear weapons, does that mean he would use them, exposing Iraq to second-strike retaliation?

If anyone can make a coherent case for war in Iraq, it's probably Tony Blair. Nobody doubts his powers of persuasion, least of all the man himself. He combines the lawyer's ability to marshal his arguments clearly with an actor's to make them resound. He is going to need them if he is to secure the backing of his country, his party and – perhaps the key to both those – help to persuade his fellow members of the UN Security Council to support the strategy he and George Bush agreed at Camp David last weekend.

No doubt yesterday's International Institute for Strategic Studies report will help somewhat. No, there is no evidence that Iraq has yet acquired the foreign material it would need to produce a nuclear weapon at short notice; but the chemical and biological capabilities available to a man who has already shown he is willing to use them remain deeply frightening. Nobody can read this with equanimity. The report's conclusion that "wait and the threat will grow; strike and the threat may be used" is no doubt as bleakly realistic as it's possible to be.

But it won't, of course, be enough. Any more than will the official dossier on Saddam's capabilities now expected within the fortnight. Indeed those in Whitehall familiar with its contents are already a little worried that it will seem a little anti-climactic after all the importance that has been attached to it. It's a commonplace that Mr Blair has to "make the case" for possible war against Iraq , starting today at the TUC. But to do that requires more than a factual assessment, however important, of the weaponry Saddam has and is trying to get in flagrant breach of UN resolutions. It also requires a sober, global cost-benefit analysis of the consequences of war in Iraq.

A few of those are touched on in President Jacques Chirac's long interview in yesterday's New York Times. The interview affords some encouragement to the pro-war party. Spectacularly liberated from the very electoral factors which are currently constraining the German Chancellor, Gerhard Schröder, Mr Chirac clearly wants to be seen as a friend of the US who is not ruling out military action against Iraq. His proposal for a two-stage United Nations process – one to set a deadline for Saddam's admission of weapons inspectors, another to decide what to do if he refuses – is a movement, perhaps decisive, in the Blair-Bush direction.

But there are caveats. The French President still purports to see Blair-Bush as located on one side of a divide in the international community, with Germany and France on the other. He is publicly brutal in his rejection of Vice-President Dick Cheney's dismissive remarks about the pointlessness of UN inspections. More significantly, he challenges the "extraordinarily dangerous" doctrine of pre-emptive, rather than retaliatory, action. What would happen if China decided to take such action against Taiwan, he asks. Or India against Pakistan? And he is unconvinced by the case for "regime change" at the very least without establishing a clear and present danger to the wider world. Avowedly less interventionist than Tony Blair, he adds: "If we start saying 'we can't accept', soon half the countries of the world will be fighting the other half."

This doesn't mean that in time President Chirac and, given his powerful personal attachment to his relationship with the US, even President Putin might not come round – at least to the point of abstention rather than a veto – to the delivery of a clear military ultimatum to Saddam, provided, that is, that it is directly linked to Baghdad's refusal to allow workable UN inspections. If they don't, and Tony Blair were to be presented with the deeply unpalatable choice of backing unilateral action by the US, against the declared opposition of figures ranging from James Baker to Henry Kissinger, then it would be much more difficult for the British Prime Minister to contain opposition, and not only in his party. But if they do, producing an explicit UN Security Council resolution backing military action, much, though not all, of the domestic opposition, not least in Britain, is likely to be dissipated. The resolution passed yesterday by the TUC in Blackpool, for example, explicitly condemned not all military action but all military action not endorsed by the UN Security Council.

But what the continuing Chirac reservations underline are the wider questions that need to be answered in "making the case". Has the old doctrine of deterrence simply been superseded? Even if Saddam had, or were on the point of acquiring nuclear weapons, does that mean he would use them, exposing Iraq to the second-strike nuclear retaliation that would devastate his country? Is he, in other words, mad as well as bad? Of course, there is a strong argument that a nuclear threat from Saddam would not conform to the old Cold War certainties of mutually assured destruction. But it will need to be made in some detail.

Then there is the question of how Iraq relates to – and perhaps even distracts from – the "war against terror" when no firm evidence exists of a link between Saddam and the terrible events of a year ago tomorrow. And what is the democratic outcome President Bush insists he wants for a post-Saddam Iraq?

But looming far over all this is the wider consequences for the region. This isn't only a matter of the outcry from the Muslim world at a perceived and wilful double standard which leaves Israel, also in breach of key UN Security Council resolutions, still enjoying the support of the US, though that's part of it. It's also a matter of what the consequences for the region would be given that Israel has indicated that it will not, as it did, during the last Gulf War, remain on the sidelines of the conflagration. All this needs to be answered, and will certainly be asked if Parliament is reconvened as it surely should be, perhaps at the time when the British government publishes its famous dossier.

This isn't, at the risk of repetition, to say that these questions can't necessarily be answered by Mr Blair. At the beginning of August it looked quite probable that the unilateralists would prevail in Washington and that the US administration might well simply brush aside any further attempt, however short-lived, to insert the weapons inspectors into Iraq. Mr Blair can claim a decent part of the credit for last weekend's decisive, if fragile, attempt to internationalise the strategy on Iraq. He has also pressed – by all accounts including last weekend – for some revival of a peace process in the Middle East, though with much less evidence so far of any will by the US to engage seriously in making the prospects for that any less bleak than they have now become. Mr Blair's moral determination that the threat from Saddam must be dealt with is said to be as fixed as it was long in the gestation – since well before 11 September 2001. But there are still many questions. And in a mature democracy the public and its elected representatives are entitled to some answers before they commit British troops to war.

d.macintyre@independent.co.uk