It was heralded as the biggest gamble of his career, a huge political risk, a make-or-break moment.
So with the Iraq war now over, has the gamble paid off for Prime Minister Tony Blair?
While Blair has earned admiration and respect in the US for supporting President Bush's campaign to oust Saddam Hussein, it has been a very different story at home and in Europe.
Though broad opinion polls have swung back in his favor ever since the first shots were fired in Iraq, Blair has alienated an important segment of his own Labour Party, offended Muslims, and upset key international partners such as France and Russia.
The British leader, who marked his sixth year in office last week, has a lot of bridgebuilding to do, analysts say.
The extent of his domestic discomfort was apparent from local elections last week in Britain. Incumbent governments often struggle in these mid-term polls, but Labour's result was anemic, the party garnering only 30 percent of votes cast, compared with 34 percent for the opposition Conservatives. Tory leader Iain Duncan Smith exulted in what he called Labour's worst showing since 1979.
Of particular note was the collapse of support across central England among large Muslim populations incensed by the war.
"Young people and the Muslim community feel that their voice was completely ignored by the government when they came out in their millions to protest the war on Iraq," said the left-wing Campaign Group in reaction to the elections. "Now they are returning the compliment and deserting Labour at the polls."
Of equal note was the message from British voters that it's the quality of life in Birmingham and Bristol - not Baghdad and Basra - that matters most to them. Blair tried to stress recently that he was putting "100 percent" effort into improving shabby public services - but voters were unimpressed. "The backlash was against a faltering economy and the Labour government's failure to improve public services," says Anthony King, professor of government at Essex University. "The prime minister has been much less focused on domestic business recently."
The other problem stemming from the Iraq war is that most Britons do not believe it has reduced the likelihood of a terrorist attack. A poll last week showed that 6 out of 10 people fear that Britain has made itself a bigger target for fundamentalist strikes.
The war "hasn't helped in keeping the coalition against terror together and keeping the Muslim countries on board," says Prof. Paul Wilkinson, an expert in terrorism and international relations at the University of St. Andrews. "Al Qaeda can use the invasion of Iraq as a propaganda weapon, so in the longer run it [the war] does create a danger of more terrorism," he adds. "This has set back British relations with the Muslim world."
Much still depends on what happens in Iraq in the coming months. If the country emerges from Saddam Hussein's tyranny as a thriving democracy, if weapons of mass destruction are ultimately unearthed, if progress in Iraq helps foster regional stability, Blair will appear vindicated, his credentials as a statesman enhanced.
But such an assessment is still a long way off.
"It's too early to say whether it's paid off for Blair," says Professor Wilkinson. "The jury is still out on the long-term consequences of the war. In the short term we have seen the toppling of a nasty dictator, and that must be a strong gain. But the pleasure at seeing the overthrow of a tyrant has to be qualified against all the uncertainties."
One of the major uncertainties, for Blair at least, is Europe. The row over Iraq has poisoned British relations with some continental powers, in particular France, dealing a major blow to Blair's efforts to position his country at the heart of the European Union.
This was, after all, the British prime minister who hoped to lead his country into the euro zone, who assiduously nurtured close ties with Russia, and who had set himself up as one of the most pro-European British prime ministers of the modern era.
Now much of that is in tatters. Russian President Vladimir Putin openly mocked Blair at a meeting last week. At the same time, peeved antiwar powers France and Germany were provocatively ramping up efforts to set up a new EU defense force separate from the US-dominated NATO.
As for the euro, the issue will likely be postponed, as Labour advisers counsel that Blair cannot risk a second unpopular crusade so soon after Iraq.
"Clearly problems have developed in his relations with the rest of Europe," says Wyn Grant, professor of international relations at Warwick University. "France and other countries in Europe see that Britain has allied itself much more closely with the US."
Patrick Dunleavy, professor of government at the London School of Economics, believes that Blair's reputation may be so badly tarnished abroad that any ambitions he may have had for an international role, be it at the United Nations or EU, may have been dashed for good.
"Internationally, he will be a controversial figure, like Henry Kissinger, with 40 percent loving him and 40 percent hating him," Professor Dunleavy says. "It's hard to see what he moves on to next. A few years ago there was talk of the presidency of the EU. He could have been a major figure in international politics, but that has all gone now."