Don't underestimate the power of persuasion, argument – and evidence

Powell's presentation was like the opening speech for the prosecution in a trial – as a piece of advocacy it could hardly be faulted

It wasn't exactly Adlai Stevenson, of course. If it had been, Colin Powell would have turned to Mohammed al-Douri, the Iraqi ambassador to the UN, yesterday and asked him, just before revealing the vital evidence: "Do you, Ambassador Douri, deny that Iraq is concealing and has concealed weapons of mass destruction. Yes or no – don't wait for the translation--yes or no."

The Secretary of State was almost certainly wise not to try it. What made that moment of theatre during the Cuban missile crisis in 1962 was that the squirming Soviet ambassador Valerian Zorin, unbriefed by the Kremlin, stammered that the US would have to wait for its answer – prompting Stevenson's famous remark that he was prepared to wait "until Hell freezes over if that is your decision. I am also prepared to present the evidence in this room". It's a safe bet that instead of squirming and stammering, Mr Douri would have contented himself with a barefaced denial.

Which doesn't mean that Powell's presentation in New York yesterday wasn't dramatic. There was little to remind the worldwide audience that some of Saddam's use of his vile weaponry had taken place when the US was backing him, of course. But the new recordings of monitored telephone conversations strongly indicating a concerted cover-up of biological and chemical weapons materials, the satellite pictures before and after the visits by UN inspectors, the mindbending details of hideously deadly materials unaccounted for since the previous inspections ended in 1998 – all unveiled by the US's most credible and persuasive top official to millions of television viewers way beyond yesterday's meeting of the UN Security Council, – could scarcely have been more effective.

So dramatic was it, indeed, that it in one painful sense it cut both ways. It would be surprising if the polls did not show support for war against Saddam among those who watched it – and not only in the US. But the more persuasive the contention that Saddam has such deadly weapons becomes, the more frightening is the possibility that he will use them against those trying to deprive him of those very weapons – a point not lost on some of the more intelligent Labour MPs who watched Powell on live television yesterday.

But the one thing Powell's presentation didn't do, as last night's reaction from France so graphically demonstrated, was to galvanise the doubters in the international community into backing war, and in particular to backing a second UN resolution that sanctions it. There was a little reminder yesterday, if one were needed, just how important that remains in Britain, when the Labour MP Chris Mullin simply got up at Prime Minister's Questions and said he could not support a war without such a resolution. Though his roots are on the left, and Mr Mullin is the most independent-minded of men, he is very far from being a serial goader of the Prime Minister. On the subject of Iraq, he speaks for the mainstream of his party.

General Powell was probably right to leave the suggested links with al-Qa'ida to the end, for they inevitably count for less than the issue of weapons of mass destruction. This isn't so much because of the quality of the evidence, though much of it is circumstantial or based on hearsay or not that new. It is rather that the chances of securing a second UN resolution – surely a vital task if the US is to build anything like the kind of coalition that sustained the liberation of Kuwait, let alone ensure the domestic support needed by Tony Blair, the President's staunchest ally – depend on persuading France, Russia and China that Saddam is in violation of the earlier resolution, 1441. And that means convincing them that Saddam has the weapons that he keeps denying he has, most recently in his curious interview with Tony Benn.

And on this, the impact of Powell's presentation, shouldn't be underestimated. A Gallup poll this week found that 63 per cent of Americans said they were more likely to trust Powell than Bush on Iraq policy, compared with 24 per cent who would be more likely to trust the President. As at home, perhaps, so abroad.

Yet formidable in many respects as General Powell's presentation was, a great deal still depends on Hans Blix. Last weekend in Washington, Tony Blair, by all accounts, pressed the President hard on the need for a second resolution – as well as, with equally uncertain outcome, for a new initiative to reignite the Middle East peace process (something that will clearly only come after a war in Iraq – if then). But Bush wasn't even prepared, after the meeting, to adopt the formulation that a second resolution was his "preferred" option.

Indeed, it was differences over that very point that is believed to have caused the 30-minute delay before the Bush-Blair press conference. That isn't because the President wouldn't ideally prefer a resolution; it's rather that he isn't sure that he will get one within what Washington regards as reasonable time, perhaps as early as the end of this month.

The emphasis laid after General Powell's speech yesterday by the French Foreign Minister, Dominique de Villepin, on reinforcing the inspectorate will no doubt fuel these fears. It took weeks of painstaking negotiation to get 1441, it's argued in Washington, and that luxury may not be available this time. And assuming no last minute backdown by Saddam, the President looks determined to invade even if he doesn't get his resolution.

The chances of securing a resolution still almost certainly depend more on Mr Blix's report to the Security Council of Valentine's Day than on General Powell yesterday. If Blix paints in still more vivid colours a picture of obfuscation by the Iraqi regime, if he leaves little doubt that he too now thinks Iraq is in material breach of 1441, then it's possible that the other permanent Security Council members, France first and foremost, will finally and reluctantly back a resolution specifically sanctioning war.

But if Blix were to hint once again that he needs more time, or if – an even more hypothetical possibility – he were to suggest that Baghdad has increased its co-operation, then France, among other countries, would seize on his report to argue for more delay. And this would leave Tony Blair in the nightmare dilemma of deciding whether to back an invasion that might not be sanctioned by a majority in his own party, let alone in the British electorate.

Mr Blair isn't a fool; he knows how unpalatable that would be. But he also thinks after his talks with President Chirac, in which the French President was careful to leave his options open, that a second resolution is wholly possible. Nevertheless, there is a way to go. Yesterday's presentation was like the opening prosecution speech in a criminal trial – as a piece of advocacy it could hardly be faulted. But it will almost certainly require the expert witness, in the shape of Mr Blix, to persuade the jury, British public opinion included.

d.macintyre@independent.co.uk