Nato has lost an enemy over the last 17 years and has not yet found a new role to justify its continued existence. Its summit meeting in Riga is the first to take place within the territory of the former Soviet Union.
And its presence there still riles President Putin of Russia, as do the invitations by President Bush yesterday to former Soviet republics such as Georgia and Ukraine to persevere with their efforts to join Nato.
The principal tension at this summit is between the US view that Nato's new role must be part of a global fight against terrorist subversion and European states, led by France, which reject that vision in favour of a rebalanced transatlantic security relationship less open to the objection that the alliance pits the West against the rest of the world.
"Out of area or out of business" was coined as a slogan for the forward policy of projecting Nato power outside Europe after the end of the Cold War. Its first real test is in Afghanistan. Nato has this year taken over from the ad hoc coalition of the willing led by the US which invaded the country and toppled the Taliban regime after the 9/11 attacks in 2001.
This summit must decide whether to strengthen the 30,000 strong Nato force there by supplementing these numbers and making their deployment more flexible. As British prime minister Tony Blair said yesterday in Riga, the alliance's credibility is at stake in Afghanistan. It is by no means obvious that Nato is winning the battle against a resurgent Taliban, while the flow of opium from there has never been higher, bolstered by warlords empowered by the original invasion.
France wants to see the country's neighbours drawn into a contact group to help the Afghan mission achieve its objectives. That would include Iran, a difficult step for Mr Bush, who resists such an engagement in Iraq.
Nevertheless the parallel difficulties faced by the US in Afghanistan and Iraq require the military and political co-operation of neighbouring states. Agreement on this question may be one of the compromises reached in coming weeks after the cross-party congressional Iraq Study Group reports on the policy options faced by the administration there as civil war comes nearer and nearer.
Extending Nato's role globally runs the central risk of associating all its members with US power projection when that has never been so unpopular or ineffective. Most European states believe such a role would undermine the United Nations, which has a far superior claim to universal legitimacy.
It would also prevent the European Union developing military, security and foreign policy capacities capable of rebalancing the transatlantic relationship and devising more effective policies, particularly towards the Middle East. The rivalry between EU and Nato institutions and forces in Brussels reveals the geopolitical tensions at play. The two overlap and co-operate, as in Kosovo; but there is as yet no consensus on Nato's future role.