It's likely to be a bittersweet parting

for two leaders who will be

forever linked by the Iraq war

Their dream of remaking the Middle East

has turned into a nightmare

Their popularity has evaporated

Their places in history are already sullied

In return for helping to oust the Taliban

in Afghanistan and Saddam Hussein in Iraq,

Blair hoped that Bush would commit the US

to bringing peace to the Middle East and that,

between them, they would leave the world a better place

The mayhem that has been unleashed across the region

is proof of the arrogance of their misjudgement

and a measure of how far they failed

Yesterday saw the start of the penultimate act of this extraordinary six-year collaboration, which has seen the Anglo-American alliance as close as any time in history.

Blair has paid a high price for his friendship with Bush, but he's back at the White House to say goodbye to his wartime ally.

It's likely to be a bittersweet parting for two leaders who will be forever linked by the Iraq war.

Their dream of remaking the Middle East has turned into a nightmare. Their popularity has evaporated. Their places in history hinge on the outcome of the war that forged their unlikely friendship.

Blair's decision to step down next month leaves Bush alone on the world stage to defend his Iraq policies without the help of his more eloquent partner.

After welcoming Blair to the White House on Wednesday evening, Bush will host his guest at a farewell question-and-answer session with reporters today.

Blair is far more popular in the United States than he is in his own country, where he has been pilloried for his close ties to the unpopular American president.

The two will get together for a final time at next month's G8 summit in Germany. Doubtless, they will cross paths in the future but as private citizens. The meeting that got under way last night is their last serious bilateral summit as leaders.

Blair is spending less than 30 hours on US soil. But that short stay encompasses a private dinner, a first sleepover at White House and several hours of talks wrapped up by a working lunch today.

Blair is conspicuously not making time to receive the Congressional Gold Medal he was awarded in July 2003 when Iraq was not quite the debacle it is today.

Those were the days - days of barbecues and jeans, days of country walks and Colgate, days of informality and innocence.

How distant they seem now. Six years on from that first, cheery Bush-Blair summit at Camp David, the special relationship has a tired and tarnished look. The two leaders meet now in largely formal settings, in business suits and beneath flags. Isolated in their own countries, older - and perhaps a little wiser - they stick together for comfort.

In travelling to Washington to make his farewells, Tony Blair has underlined the change. How long ago is it that London was a US President's natural staging post on his way to and from the rest of the world?

Since Iraq started to go wrong, Mr Bush has done Mr Blair the courtesy of preferring Warsaw or Berlin. An alliance whose closeness was once the envy of other Europeans had become just too much of a political liability in Britain.

We know at once too much (thanks to our former ambassador in Washington, Sir Christopher Meyer) and too little (because Sir Jeremy Greenstock, Britain's former ambassador to the UN, has not been allowed to publish his memoirs) about the discussions that led to the invasion of Iraq.

There is still controversy about whose zeal to remove Saddam Hussein was the greater, although Britain's inferior power and the assumption that Mr Blair was the follower not the leader saddled him with the damaging soubriquet "Bush's poodle".

Nor do we know for certain, even now, whether Iraq's supposed weapons were the real reason for the US and British military action, or just a pretext whose legality could be fudged.

And it will be for historians to judge, in the end, whether it was the invasion itself, or the failure to prepare for the aftermath, that constituted the fatal error. Those who supported the war naturally prefer the latter judgement; we incline to the former.

What is not contestable is that the war in Iraq has proved a catastrophic miscalculation that has blighted the reputations of both leaders. It casts its pall over almost anything else they might have achieved.

It is telling that a theme of Blair's day in Washington will be the agreement on power-sharing in Northern Ireland.

Africa and climate change will also feature, but not Iraq - our most significant and costly joint enterprise. Nor will Mr Blair be passing by Capitol Hill to pick up his Congressional medal, associated as it is with his support for Mr Bush over Iraq.

But it is not only the personal reputations of both leaders that have been damaged. That elusive "special relationship" has suffered, too, at both the political and the popular level.

The awkwardness was all too apparent in Gordon Brown's recent visit to the White House. Already Prime Minister in waiting, he needed to be acknowledged as such in Washington, but could not afford to be seen paying court to George Bush.

The solution was the "drop-by" - a furtive, off-camera encounter that was a sad comment on what the Bush-Blair alliance has done for bilateral relations.

That power in Washington is now divided between a discredited Republican White House and a Congress controlled by Democrats should make it easier for Mr Brown to deal with the US without seeming to kow-tow to Mr Bush.

The legacy of transatlantic relations Blair bequeaths, however, must be very far from the one he intended.

In return for helping to oust the Taliban in Afghanistan and Saddam Hussein in Iraq, Blair hoped that Bush would commit the US to bringing peace to the Middle East and that, between them, they would leave the world a better place.

The mayhem that has been unleashed across the region is proof of the arrogance of their misjudgement and a measure of how far they failed. Indy