Rupert Cornwell: America was looking for comfort, inspiration and leadership. Bush stood up and delivered

For a man not often visited by the muse of public speaking, it was the speech of his life. But for even the most accomplished of orators, it would have been the speech of their lives too. Thursday night on Capitol Hill was, beyond argument, the finest hour of George Bush's young Presidency.

Since the cataclysmic events of 11 September, Mr Bush has steadily improved his game. After the unseemly flippancy of "the folks who did this" in the hours following the attacks, he produced a decent Oval Office address that night. His words a week ago at the national prayer service were stirring, and even better were his appearances at ground zero of the devastation in lower Manhattan, and at an Islamic centre here in Washington.

There have been lapses: his reference to a "crusade" that had US diplomats squirming, and the "Wanted: Dead or Alive" stuff that made liberals laugh. But, in front of a rapt, utterly united Congress, the 43rd President performed better than even his most fervent admirers could have expected.

The atmosphere, of course, helped hugely. Democrats and Republicans alike desperately wish Mr Bush well. Everyone wants him to succeed. Differences there may be, within Congress and within his Administration, over the nature of the response – but the most malicious soul could have detected none of it as Mr Bush arrived.

Even before he entered the chamber of the House to the inimitable bellow of the Serjeant-at-Arms – "I give you the President of the United States" – they were cheering the arrival of the special guests. Like football fans reacting to the team-sheet being read out before kick-off they roared approval for Rudolph Giuliani, the Mayor of New York, George Pataki, the state's governor, Laura Bush, the President's wife, and Tony Blair.

Then, as the President gladhanded his way down the aisle, tanned and white-shirted with his favoured blue tie, you sensed something was different. You sensed he would rise to the occasion.

And how he did, swept along on a great rolling tide of national unity. Was it 31 or 32 times they interrupted him? – even the relentless fact checkers of The New York Times contradicted themselves. But when the members weren't cheering, you could have heard a pin drop. No one moved a muscle.

In the chamber and beyond, strange things were happening. For security reasons, Vice-President Dick Cheney, who would normally have sat behind Mr Bush on the rostrum as president of the Senate, was not present. The pugnacious Dick Armey, House majority leader, was also told to watch "from a secure location."

In the event, a stunning 79 per cent of Americans watched. Normally, sport eclipses politics in the national consciousness – but in Philadelphia they called off a hockey game when the fans in the arena made clear they wanted to watch Mr Bush, not the hockey players.

Speechwriters, however, can only get a politician so far. Someone has to speak the words – and one man's flashing shaft of rhetoric can be a cliché in the mouth of another. On Thursday night, if there were clichés, they didn't sound like them. Just plain language from a plainspeaking man.

"We will not tire. We will not falter. We will not fail," Mr Bush declared. "Americans are asking, 'What is expected of us?' I ask you to live your lives and hug your children. I ask you to uphold the values of America, and remember why so many have come here. We're in a fight for our principles and our first responsibility is to live by them. No-one should be singled out because of their ethnic background or religious faith."

Doubtless Ronald Reagan or Bill Clinton would have produced more striking phrases. Winston Churchill Mr Bush is not. But he struck exactly the right note. In times of crisis, Americans look to their President for comfort, for inspiration, for political policy making and military leadership. On Thursday, Mr Bush managed to be all things at once.

Gone was the maddening smirk, the nervous tics, the sense of shallowness, the feeling that he was trying to escape the camera, that he'd rather be somewhere else. Throughout the address, he never really smiled. When he mentioned individuals, he gave them a long, determined reassuring look. Under the circumstances, it was exactly right.

In simple, unadorned words, he told America who did it, why they did it, and what he proposed to do about it. He told them there would be no negotiating, just a long, unrelenting struggle to eradicate terrorism. Many may disagree with the who, the why, the what – or all three. But no one can complain of being left in the dark.

Not since 12 April 1945, when the rookie vice-president, Harry Truman – like Bush generally reckoned beforehand to have been promoted beyond his station – learnt that Franklin D Roosevelt had died, has a President faced such an examination of character. Even Lyndon Johnson's ascent in 1963 was less traumatic; however tragic the circumstances, he had sought the job for years.

As the full implications of what happened 11 days ago began to dawn on Mr Bush, he must have felt like Truman, the machine politician from Missouri whom FDR had not deigned to inform of the existence of the atomic bomb yet which Truman had to use within four months. "I felt like the moon, the stars and all the planets had fallen in on me," Truman later said of the moment he was told he was president.

Everything could yet go wrong. One good speech does not win a war. Maybe Mr Bush raised the bar too high; a conventional rule of statesmanship is always to leave one's opponents a way out.

But these are not conventional times. On Thursday night, Mr Bush slammed the door shut, promising vengeance not just on those who carried out the attack, on the Taliban and any other states which supported them. He asked every country to choose. "Either you are with us or with the terrorists... We will bring our enemies to justice, or bring justice to our enemies."

Such simplicities, his portrayal of America as innocent citadel of God and freedom, will jar on many a European ear. And great tides of unity not only rise; in time they ebb. Mr Bush warned the war would take years; something approaching political normality will return long before that. And last but not least, Afghanistan may defeat America, as it defeated Britain and Russia in the past.

But on Thursday, the President convinced his countrymen that he is up to the job. Today, Harry Truman is remembered as one of America's great Presidents. Could historians one day deliver a similar verdict on an equally improbable candidate? George W Bush?