Sobered by the chaos that has ensued in Iraq since the fall of Saddam Hussein, the US appears to be making a course correction. The Bush administration is expediting plans to return power to Iraqis and asking the United Nations to help out. Rather than confronting "rogue nations" with the prospect of regime change through force, Washington has been negotiating with Libya, Iran and North Korea.

These are welcome developments both for Americans who have bemoaned the erosion of a centrist brand of US internationalism and for people around the world who have come to resent Washington's overbearing ways.

It is too soon, however, to presume that the US is rediscovering the path of moderation. The new tack represents a tactical response to the troubles in Iraq, not a deeper strategic shift. Furthermore, secular changes in American politics, not just the idiosyncrasies of George W. Bush and his neo-conservative advisers, are pushing the country away from liberal internationalism. Even if the Democrats win the presidency this November, a more diffident and difficult America may well be here to stay.

America's embrace of liberal internationalism began in the 1940s, when President Franklin Roosevelt utilised the second world war to build a bipartisan coalition behind multilateralism. Cold-war imperatives sustained this centrist coalition for the next five decades, but it unravelled soon after the Soviet Union's collapse. By the late 1990s President Bill Clinton, although an avowed multilateralist, was hemmed in by by domestic politics, with Washington keeping its distance from the Treaty to Ban Landmines, the International Criminal Court and the Comprehensive Test Ban Treaty.

The election of George W. Bush dramatically accelerated these go-it-alone tendencies. Bereft of its internationalist wing - Bush pe`re, Henry Kissinger and Brent Scowcroft wield influence, but no longer power - the Republican party has veered towards a tough unilateralism shaped by neo-conservative ideology and the populism of the party base in the heartland. The September 11 terror attacks, far from pushing the administration back to the centre, stoked an angry vulnerability that put extremist voices in command. The moderates, Colin Powell most prominent among them, have been embattled ever since.

To be sure, the proclivities of the Bush White House are unique in important respects. Should the influence of neo-conservatives weaken or the Democrats take back the White House, the current penchant for unfettered primacy would abate.

Nonetheless, it would be illusory to presume that a change of personnel or party will bring back America's liberal brand of internationalism. A weakening of internationalist leadership is taking place across the political spectrum. The generation of Americans that fought in the second world war and oversaw the building of the west is retiring from politics, to be replaced by a generation that lacks the experience that formed the foundation of liberal internationalism. Moreover, the terror ist threat is here to stay and will continue to favour the extremes, not the moderate centre.

So too is populist politics - and its aversion to submitting America's will to the preferences of others - animating Democrats as well as Republicans. Demographic shifts are strengthening the power of the south and interior west (home of heartland populism) at the expense of the north-east home of the liberal establishment). It is no accident that the Democratic presidential hopefuls have been reaching out to voters who drive pick-up trucks.

Finally, the increasing polarisation of US politics does not augur well for the restoration of liberal internationalism. The right is moving to the right and the left to the left. Moreover, the political divide is falling along geographic lines; the coasts tend to be liberal and Democratic, the heartland conservative and Republican. An ethnic dimension, featuring a swelling Hispanic population, further complicates the picture.

The intensity of political and sectional divisions will hinder the formation of an internationalist consensus that cuts across party and region - just as such divisions did earlier in US history. Roosevelt succeeded in repairing these divides only by forging a coalition of moderate Democrats and Republicans and building an unprecedented alliance between north and south. With today's Democrats and Republicans engaged in trench warfare, the restoration of a bipartisan centre appears to be a remote prospect.

The worst of America's excess on the global stage may be behind us. But the task of bringing the US back to a liberal brand of internationalism is just beginning.

The writer, a professor of international affairs at Georgetown University and a senior fellow at the Council on Foreign Relations, is author of "The End of the American Era"