Solemn Bush drops the swagger to put his resolve on show

The language was eerily – and beyond doubt deliberately – reminiscent of President George Bush in those numbing days immediately after 11 September 2001.

Then, the President caught America's yearning for revenge by declaring that the war which al-Qa'ida had launched against the US would end "in a way, and at an hour, of our choosing". And so it will be now with Saddam Hussein. Assuming that he declines the urgent invitation to leave his country by tonight, America will unleash its armies to remove him "at a time of our choosing".

The phrase is a typical coinage of Michael Gerson, the chief White House speechwriter whose brilliant endeavours are worth a dozen Marine divisions to his master: sonorous, slightly archaic, with a vaguely religious cadence.

Most importantly, though, the repetition subtly underlines the message at the heart of Mr Bush's 15-minute television address on Monday night: that the invasion that will probably be under way by the end of the week is the logical, linear next step in the war against terror that began on 11 September.

The atrocities in New York and Washington are being used to justify the biggest foreign policy roll of the dice by an American President since John Kennedy confronted Nikita Khrushchev in the 1962 Cuban missile crisis. They spawned the new doctrine of "pre-emptive response", which is being roadtested for the first time against Iraq. And in Mr Bush's long-since-made-up mind, they bestow on America the right to go to war in an especially volatile region, without the explicit backing of the United Nations, in the teeth of public and governmental opposition around the world.

As Bush public speeches go, this one was grim and measured. It displayed both the worst and the best of this President – the narrowness of vision, the reluctance to entertain opinions other than his own; but also the resoluteness and decisiveness that made him so effective a leader in the weeks and months after the World Trade Centre attacks.

He was appropriately solemn. The tone was "more in sorrow than in anger", and only once did he invoke the Almighty, in his final line that "God continue to bless America". There was none of the "make my day" swagger that often passes for Bush diplomacy, none of the smirking cockiness that foreigners in particular cannot abide. But he seemed more animated than at the parody of a press conference on 6 March, when he gave pre-cooked answers to pre-selected questioners who were allowed no follow-ups.

At home, an uneasy country is closing ranks behind Mr Bush as it always does when its soldiers are about to go into battle. At least for now, anxiety over acting without explicit UN approval is fading. A CNN/USA Today poll found that, by a two-to-one margin, Americans support the 48-hour deadline for President Saddam and his sons to leave the country; a similar proportion believes that Washington has done everything to resolve the crisis by diplomatic means.

But beneath the surface, apprehension and disagreement simmer. For all Mr Bush's moral certainties and his talk of a "broad coalition", many Americans are disturbed by the lack of international backing. Tom Daschle, the Democratic leader in the Senate, is far from alone in his complaint at the "miserable failure" of American diplomacy that has so contributed to the impasse.

Americans may just about be persuaded by their President that Saddam Hussein is indeed a 21st-century version of Hitler and that to ignore him is to repeat the mistakes of 1930s appeasement. Most of the rest of the world finds the comparison ludicrous. "The security of the world requires disarming Saddam," Mr Bush told his people, speculating on Iraq's "power to inflict harm on all free nations". But other "free nations" are hardly quaking in their boots at the prospect of an attack from a clapped-out, sanctions-ravaged small power in the Gulf.

The President claimed as his own the right to act in the name of the world in the name of a global emergency. Unfortunately, much of the rest of the world does not see things that way, now matter how much his administration distorts the facts to persuade it.

Events these past few days have only underlined how truth is the first casualty of war – even before the shooting has started. At the weekend, the Vice-President, Dick Cheney, was claiming, contrary to every shred of evidence and the assertions of Mohamed al-Baradei, the chief UN atomic energy inspector, that Iraq had "reconstituted" nuclear weapons. Documents brandished by his officials purporting to show Baghdad had been buying uranium in Africa have been revealed as crude fakes.

On Monday, Mr Bush again claimed there were close links between the Iraqi regime and al-Qa'ida (an assertion repeated so frequently that half of all Americans believe that President Saddam had a hand in 11 September, despite not a shred of evidence to that effect). The President warned that the Iraqi leader would use chemical and biological weapons against the world; the CIA has said Iraq would only use them in extremis, against an invader.

But, once again, the "fear factor" comes into play, and the memory of 11 September is invoked to answer every doubt. This time the President raised the spectre of terrorist attacks on American targets, both abroad and at home, ordered by President Saddam's regime in its death agony. They were, he conceded, not inevitable, merely "possible" – but "this very fact underscores the reason we cannot live under the threat of blackmail".

And even as Mr Bush spoke, the Department of Homeland Security cranked up the colour-coded danger alert level from yellow to orange. The last such move, in February, led to the great duct-tape and plastic sheeting fiasco. Yesterday, Tom Ridge, the head of the department, urged calm. But he announced new measures called "Operation Liberty Shield" which is hardly likely to soothe the public's jumpy nerves. With war imminent, such precautions sound reasonable. But Mr Bush and his political handlers know full well that the "terrorism" card is a trump that can be used to justify almost any measure and explain away almost any failure.

Playing to perceived Republican competence in the national security field, the card is an important potential asset for Mr Bush in the 2004 re-election campaign.

But that is for the future. First Mr Bush has to win his war, and win it well and quickly. On that everything depends, including his presidency.