One issue will dominate the Nato summit this week in Riga: Afghanistan. The 26 prime ministers and presidents must decide how to respond to the challenge facing the 32,000 Nato troops deployed with the International Security Assistance Force (Isaf), which is hard pressed in fighting the resurgent Taleban and in trying to extend the Kabul Government’s authority. For although all members have contributed troops to the Nato operation, only a few have sent troops to the turbulent south, where, understrength and underequipped, they have come under intense attack. President Bush and Tony Blair want those members reluctant to move their forces from safer and more comfortable deployments in the capital — especially those of Germany, Italy, France and Spain — to pull their weight and join the stretched Britons, Canadians, Dutch and US troops in the south.

Unfortunately, too many European countries sometimes find it easier to criticise than to contribute. They declare themselves ready to help to stabilise Afghanistan, but are unwilling to risk the opposition of sceptical public opinion, which is as defeatist in its assessment of the mission as it is hostile to joining the US in active operations. There will be excuses and prevarications, but President Bush’s weakened political position make it unlikely that his European allies will change their present pusillanimous stance.

Those who have demonstrated most pluck and responsibility are the newcomers. The Poles, Hungarians and the Baltic states, among others, have shown a commitment and seriousness about their Nato pledges that ought to shame the larger, wealthier and older members. For them, however, Nato still offers not only a strong underpinning to democracy, human rights and Western values but also a protection against the old dark forces that they recently left behind.

Since the collapse of communism, the alliance has been eager to reinvent itself as a force for regional stability, to quell threats to peace within Europe and, as in Afghanistan, beyond. Its new members still value Nato for its original purpose, as a bulkwark against Soviet aggression. Having endured occupation or the subsuming of national independence within a Soviet empire, they are still deeply suspicious of Moscow’s intentions. Much of the corridor talk during this first Nato summit on former Soviet soil will be of the renewed threat from Russia.

Moscow’s aggressive use of energy as a political weapon is the most obvious cause for concern. Most of Nato’s members, especially the Baltic states, are worryingly dependent on Russian oil and gas. And for all Russia’s assurances that it will be a reliable energy partner, the threats and interruptions to supplies to Ukraine, Georgia and the Baltic states suggest a far less reassuring reality. Nato leaders will be asked to look at possible action to avert potential threats to energy sources by patrolling key shipping lines, or resupplying a victim of an energy suspension. That is a sensible updating of the doctrine of mutual military aid. But Nato ought also to revisit some of its Cold War strategies for dealing with pressure and destabilisation from the East. As the Litvinenko affair has shown, Mr Putin’s Russia is brash, newly self-confident and not afraid to strike at imagined enemies. Nato must still be prepared to protect its members from all such dangers.