The wisest statesmen are those who mask their setbacks and embrace decisions that go against them. The presidents of Georgia and Ukraine have clearly understood how to navigate the shoals of multilateral diplomacy. Though their faces betrayed their disappointment, they insisted in Bucharest yesterday that Nato's promise of eventual membership at some unspecified date, rather than the immediate offer of a membership action plan, was nevertheless an “historic breakthrough”. President Bush, their most forceful champion, also declared that Nato's door must remain open to other nations in Europe.

There is, however, no disguising the fact that the refusal of Germany, France and some other member states to endorse the US call for a start to membership talks with the two former Soviet republics is a rebuff to Washington. It also reveals deep splits within the 26-member organisation on what Nato stands for and what its relations should be with Russia, the giant Eastern neighbour whose bellicose policies gave birth to the alliance 59 years ago. Since the fall of the Berlin Wall, Nato has been searching for a new purpose and relevance. The original members recognised that a mutual defence pact to protect themselves from Soviet expansionism was no longer needed. But in decades of working together, they found that the pooling of defence policies had also brought tangible benefits: shared procurement policies, strategic thinking and democratic values. To continue these gains, Nato therefore transformed itself into a regional security guarantor and an institutional yardstick by which freedom might be measured and enhanced. The logic, therefore, was to open Nato to all those newly sovereign former communist countries, to embed their democracy, underpin their independence and enforce regional stability.

Sadly, the alliance has made a poor job of explaining this transformation to its own members or to its former adversary. Its leaders insist that Nato is not an anti-Russian league to push Western dominance farther east and encroach on Russia's interests. Its newest members, however, see the main purpose of joining still as a defence against their former oppressor, a guarantee that Russia can no longer encroach on their interests.

This partly explains the differences on how to deal with Russia between most of the original members, worried that Russian hostility will diminish rather than enhance European security, and the new members who believe that Moscow's bullying must be forcefully rebuffed. To delay opening membership talks with Ukraine and Georgia because of divisions within those countries over membership may be reasonable; to do so out of fear of Russian reaction is unacceptable, a craven capitulation to President Putin.

In this debate, one voice has been notably, embarrassingly, absent. Gordon Brown, attempting to sit on the fence, has missed a huge opportunity. He could have taken a lead in explaining to Moscow the need for a Europe-wide alliance. He could have shamed Germany into a more robust defence of freedom in the East. And he could have urged sharper diplomacy on Mr Bush. Britain must remain at the heart of Nato in its new role. Instead, it has slunk to the sidelines, letting other determine strategy and policy. Mr Brown has put himself and his country at the heart of this Nato summit's historic non-decision.