Tony Blair has defined a decade of British politics, but pinning down his legacy can be an elusive pursuit.

Domestically, Blair made an art of "big tent" politics to dominate the political center. His secret was creating policies that were often more social-democratic than his political language implied.

He refused to concede issues like crime and immigration to the right. But his government married economic liberalism with a strong social agenda.

So, while Blair is often defined by his unflinching support for U.S. foreign policy, his Britain is best understood as a mid-Atlantic project - maintaining Anglo-Saxon competitiveness but seeking to mitigate its sharp edges with a more Scandinavian social agenda.

Blair was lucky in his political opponents. He was nine years in office before the Conservative opposition began a serious inquest into its three general-election defeats. Now, under David Cameron, the Conservatives seek to emulate Blair, at least rhetorically. A British right which has to disown its Thatcherite convictions is a significant Blair achievement.

But Blair's legacy is also to leave British foreign policy in flux as rarely before. Iraq dominates all discussion of the Blair record.

The intelligence failures over WMD and the disastrous failure of postwar planning mean that Blair's insistent defense of the overthrow of Saddam has become an increasingly lonely one.

Blair remains convinced he was right. But even in his own terms, the war marked the failure of his foreign policy. He took office determined to end Britain's half century of ambivalence about its role in Europe and to show that a choice between the United States and Europe made no sense for a nation defined by its global links.

Yet Blair's bridge collapsed: He had to choose, leaving his European mission unfulfilled. The broader tragedy of Blair's foreign policy is that this eloquent advocate of liberal internationalism may have done lasting damage to this cause.

If Iraq was a pre-emptive intervention which lacked legitimacy, Rwanda and Darfur demonstrate the price of inaction. The Blair doctrine - set out in his Chicago speech of 1999 on "new rules for the international community" - made legitimacy and an effective multilateralism central to resolving this.

In later stressing his shared values with American neocons, Blair missed some sharp differences between their political project and his own. For Blair, the effective use of military power depended on an equal emphasis on reconstruction and development. Donald Rumsfeld and Dick Cheney did not agree.

There will be continuity in many areas of policy under Gordon Brown - this has been a Blair-Brown government, after all. But Brown knows that a decade-old government also needs significant change to reconnect with voters.

Blair and Brown share the view that Britain has most to lose from a retreat from globalization. But Brown is instinctively cooler towards Europe than Blair and, while he is a committed Atlanticist, he faces significant pressure to demonstrate more independence from the United States.

A sharp reversal of Iraq policy is unlikely. But a gradual disengagement will likely be combined with a renewed commitment to a secure settlement for Israelis and Palestinians, and perhaps dialogue with Iran. Brown is likely to emphasize soft power, including a new cultural front in tackling extremism.

None of this marks a fundamental break with Blair, but British foreign policy may well feel rather different. Despite the clarity of Blair's world view, he leaves office perceived as having largely lost the public argument. That means that his successor will need to rebuild the public consensus on Britain's global role.

Sunder Katwala is general secretary of the Fabian Society, a leading center-left British think-tank. This piece was published in the International Herald Tribune on 10th May 2007.