Rupert Cornwell: This is a gamble of massive effrontery to the voters, the politicians and even the generals

There is one thing that is certain: this war, from now on, is President Bush's war alone

American politics offer few sights more magnificent than Ted Kennedy in full flow. Irredeemably liberal he may be, as he approaches his 75th birthday, but the Massachusetts Senator is a monument to history as no other living US politician, with his legacy of legislative achievement and burden of family tragedies. And this week, Mr Kennedy waxed eloquent about another tragedy, this one unfolding. "Iraq," he warned at the National Press Club, his white mane of hair quivering in rage, "is George Bush's Vietnam."

Vietnam, of course, was Lyndon Johnson's war. But its shade has been almost tangible in Washington as this President has honed his plans to send more American troops to salvage something from the wreckage of Iraq. I write before Mr Bush delivers his fateful address, incomparably the most important of his six years in office, and perhaps the most difficult delivered by any president in the past three decades.

I do not know whether he will define his goal as "victory", "success" or whatever. I do not know whether he will talk about a "surge", or a "temporary increase", in American strength in Iraq - though, sure as anything, he won't use the term "escalation", with all that word's overtones of Vietnam. One thing I do know, however, this war, from now on, is Bush's war alone.

He won't necessarily mind that. He prides himself on his refusal to bow to prevailing winds, and takes solace in the belief that history's judgement on him will be kinder than today's opinion polls. Harry Truman, who left office reviled but half a century later is generally counted in the small company of "near great" presidents, is Mr Bush's model. But what he sees as steadfastness under fire is more exactly a gamble of massive effrontery.

By sending more troops, he is ignoring the result of November's mid-term election, when voters sent the Republicans packing because they had enough of a war without visible results or visible end. He is giving a polite two fingers to the Iraq Study Group, the bipartisan blue riband committee that only last month recommended that almost all US combat forces should be out of Iraq by early 2008.

He is making an even ruder gesture to the Democrats, less than a week after they took command of Congress. So much for all that talk of bipartisanship; for Mr Bush, he has shown that, once again, bipartisanship means his political opponents doing what he tells them. He is also ignoring respected voices in his own party, such as John Warner, the straight arrow, immensely experienced former chairman of the Senate Armed Services Committee, one of the strongest supporters of the original 2003 invasion, but who now believes sending 20,000 extra troops would be futile.

Last but not least, a president who has always made so much of how he always follows his commanders' advice has overruled his joint chiefs of staff who see no point in committing even more of an overstretched military into a civil war which the US presence only exacerbates.

General John Abizaid, the top commander for Iraq, publicly stated last year that boosting American forces would achieve nothing. He has been prematurely retired. Operations on the ground will be now be run by Lieutenant General David Petraeus, a supporter of a larger US force - and, by no coincidence, arguably the army's top expert on counter-insurgency.

For that is what the US campaign in Iraq basically now is: an expanded effort to stamp out insurgents who have succeeded in provoking a civil war. I write before Mr Bush has defined the mission of the enlarged force - if indeed he does define it: how long the troops will stay, what "benchmarks" for political and security progress the Iraqi government must meet, and when the long-term withdrawal of US troops will begin. But the odour of that failed earlier counter-insurgency war in Vietnam is inescapable.

General Petraeus has just put together an updated counter-insurgency warfare manual for the US Army. It is a fascinating document, in which two basic points shine through. First, military measures alone cannot suffice: they must be meshed into an overarching political plan. Second, counter-insurgency wars, by their nature long drawn-out affairs, must have political support at home.

Neither condition was met in Vietnam, while in the case of Iraq, the domestic front crumbled long before Mr Bush went on television last night. Almost two thirds of Americans oppose a troop increase, his handling of the war is backed by only 26 per cent of voters, and his own approval rating is a bare 37 per cent, according to a Gallup Poll. Not exactly a platform from which to rally the country to his cause.

As for the political plan to go with the new military push, Mr Bush has bet the ranch on Nouri al-Maliki. This is the same Iraqi Prime Minister whose parliamentary majority depends on Muqtada al-Sadr, the radical cleric whose militias are more powerful than the official Iraqi army, and the same Prime Minister who fanned the sectarian flames by sending Saddam Hussein to his rushed and barbarous death; again, not exactly a man an American president would normally choose to go tiger shooting with.

And once again, warnings voiced in Vietnam echo down the years. "We can't run this thing. They've got to run it," said General Creighton Abrams, the top US commander in South Vietnam between 1968 and 1972. Those were the years of "Vietnamisation", when the total US force shrank from 535,000 to 30,000. In Iraq, by contrast, albeit from a much smaller base of 132,000 troops, Mr Bush wants to increase that number by a reported 20,000.

To straddle this gap, the White House simultaneously is desperately, and absurdly, pushing the idea of "Iraqisation". As one of Mr Bush's top aides managed to claim with a straight face of the President's plan: "This is an Iraqi initiative, but an initiative which requires our support."

Buy that and you'll buy anything: that the Bush administration actually believes in Mr Maliki, that the Iraqi Prime Minister will turn against those who are keeping him in power, and that Shias and Sunnis will soon lie down together like lambs, having seen the folly of their ways.

But it is too late now to banish the folly of this war. Some still maintain that the initial invasion was right, and that had the occupation been better handled in the vital first weeks and months, some kind of Iraqi national reconciliation could have been achieved. But even these believers mostly consider Mr Bush's latest prescription to be much too little, much too late.

Far better that he admits his error and cuts his losses. But most politicians, and least of all this American President, are capable of admitting error. Thus, the Iraq tragedy will continue, with events there and in the region spinning ever more beyond America's ability to control them.