Mr Blair has proved his loyalty to President Bush - but not the case for war

Among the signal strengths of our Prime Minister are presentation and the ability to persuade, and the marathon press conferences he has introduced show off these qualities to the full. But they do not make his every word convincing, nor do they mean that real questions do not remain. Yesterday's 90-minute session, held in his Sedgefield constituency only hours after his return from the Earth summit in South Africa, was no exception.

Tony Blair's latest exchange with the media demonstrated how substantially the political mood has changed over the summer on either side of that famous Downing Street front-door. Yesterday's questions established how Iraq now dominates the national political discussion. The Prime Minister can be in no doubt, if ever he was, that the prospect of Britain joining a US attack is, and will remain, a matter of media and public concern until it is resolved one way or the other.

Mr Blair, for his part, assumed a decidedly more Atlanticist stance than at any time since the immediate aftermath of 11 September. He let slip no opportunity to stand, metaphorically, shoulder to shoulder with the United States and with President Bush. America, he insisted several times, should not have to face the issue of Iraq alone. He blamed criticism of the US, particularly in Europe, largely on "anti-Americanism", and added for good measure that the George Bush widely depicted in the media was a "parody" of the serious American President that he knew.

Mr Bush, presiding as he does over a Cabinet and Congress now openly divided about the merits of military action, can take succour from Downing Street's renewed expressions of almost unconditional loyalty. The beleaguered state of the Bush administration on Iraq may indeed be the main consideration behind Mr Blair's rhetorical shift; the increasing global isolation of Washington afforded Iraq an opportunity that it was only too ready to exploit.

But the Prime Minister is steering a perilous course here. The closer he veers towards Washington, the greater the risk of his own isolation – first in Europe, where governments have spoken out with rare unanimity against precipitate action against Iraq; second, within his parliamentary party; and third and crucially, in the country at large. There are times when such political isolation is noble and right – as the US Defence Secretary, Donald Rumsfeld, recently tried to suggest in his misguided Churchill analogy. But nothing that Mr Blair said yesterday, including his highly questionable assertion that the 11 September attacks could equally have been directed at London, Paris or Berlin, conclusively makes the case against Saddam.

For all the "beliefs" that Mr Blair expressed yesterday, he offered not a shred more evidence that Iraq currently presents the "real and unique threat" (his words) that would justify urgent military action. He invoked the mortal dangers presented by an Iraq armed with chemical, biological and nuclear weapons without pinning down whether Iraq possessed such capability, was on the verge of possessing it or merely harboured such ambitions. Always there was something short of certainty: a "belief", a "probably", a "doubtless". And he again temporised on publication of the dossier on Iraq's military capacity, promising it "within a few weeks".

Such a standard of proof may satisfy an anxious American public on the eve of the 11 September anniversary. But the British public wants, and should have, something more credible.