World View: Nato was famously defined in the 1950s by its first secretary general Lord Ismay as an organisation designed to "keep the Russians out, the Americans in and the Germans down" in Europe.
Since the end of the cold war the Russians remain out, but transformed, while the Germans are reunited and a regional power. The Americans are still in - but does that objective suffice to keep the military and political alliance in which they are the dominant partner together? This week provides ample evidence that it does not, and that other commonly agreed objectives are hard to find.
US secretary of defence Robert Gates repeated his warning that Nato is in danger of becoming a two-tier alliance if more troops are not provided by European members to fight in Afghanistan. It cannot survive if one group of members - currently the US, Canada, the United Kingdom, the Netherlands and Denmark - provide the bulk of the fighting troops there, while others provide only back-up forces. "Such a development, with all its implications for collective security, would effectively destroy the alliance," he said.
He went on: "I am concerned many people on this continent may not comprehend the magnitude of the direct threat to European security. The threat posed by violent extremism is real - and it is not going away." The arrest of 14 extremists recently in Barcelona suspected of planning attacks on public transport systems in Spain, Portugal, France, Germany and Britain is an example of what is involved, he said. But because many Europeans do not see the relationship between Afghanistan and such threats, they are not prepared to provide fighting troops or want them removed.
German public opinion is against allowing their troops in Afghanistan adopt a combat role in the south rather than the training and reconstruction tasks they have undertaken in the north of the country. The US effort to harness the Nato force there into a renewed war against the resurgent Taliban is resented and opposed. German political leaders have no choice but to go along with this.
They are angry about US accusations that they misconceive their role as an armed peace corps rather than a war-fighting coalition. In Germany and elsewhere in Nato, military establishments seethe about wrong-headed US political strategy and military tactics in Afghanistan, which they regard as incapable of defeating the Taliban. US policy seems to echo that in Iraq, to impose a weak US-dominated government on a society which resents the presence of foreign troops.
The Afghan case goes to the heart of Nato's existential dilemma. It exemplifies the US effort to add another objective to the foundational three: to keep global terrorism down and out. But Europeans habitually put inverted commas around the "war on terror" to signify they do not believe in it as a global threat requiring a Nato response. They prefer to deal with terrorism by policing, border security and prevention rather than global military action. Much of this is controversial, notably border security, but it stops far short of military mobilisation. And when the US insists on radical securitisation measures for transatlantic air travel to back up their threat analysis, it only deepens European resentment.
During the 1990s, Nato enlargement went ahead of EU enlargement in response to the end of the cold war. That made sense in Europe as a way to handle security questions thrown up by the collapsing Soviet empire - especially for former Warsaw Pact states who knew Russian leaders are not reconciled to diminished power. Nato's Partnership for Peace structures extended to newly independent states.
Nato intervention in the Balkans was less consensual, so much so that US leaders were determined not to repeat it. They therefore spurned European offers of help after 9/11, running the Afghan and then the Iraq invasions as coalitions of the willing.
Their later effort to create a world role for Nato was unconvincing in the light of this history.
Besides, by then the EU was well on its way to creating its own political-military structures through the common foreign and security policy. The 10th anniversary of the St Malo military/security agreement between Britain and France, which gave that effort indispensable political liftoff, falls later this year. Britain remains a steadfast Nato power, but not at the expense of the EU structures. Sarkozy wants to bring France back into Nato's high command, but only if the EU's new policies are fully recognised, which implies a major renegotiation.
Alternative ideas like those of Edouard Balladur, one of Sarkozy's advisers, who advocates a new western civilisational union between Europe and the US to counter the growing power of Asia, will play into that negotiation. Whether and how to conduct it will be a major issue for the new US president. But any new structure is likely to be looser and more variable than Nato.
A recently published study, Growing Apart? America and Europe in the 21st Century (Cambridge 2008), highlights three major emerging differences: the role of religion in public life; the proper role of the state and supranational structures in dealing with globalisation; and attitudes to immigration. They might add different attitudes to military power and spending, in which the US outreaches all of its Nato allies combined.
Such tensions lie behind recent US offers of Nato membership to Ukraine and Georgia and efforts to place anti-missile systems in the Czech Republic and Poland to head off an alleged threat from Iran. These are pursued through partisan channels in those countries, an approach resented increasingly by mainstream EU leaders who say they needlessly antagonise Russia. But they will not necessarily be abandoned by a new US president. Either way, keeping the US in Europe looks increasingly like perpetuating an outdated form of US domination. A more equal relationship is now demanded.