IN these giddy times not a day passes without some spectacular repudiation of the Republican past by the Obama administration. Never mind the vaunted first 100 days.

The first 10 days alone have already seen an opening to the Muslim world, the abandonment of military tribunals at Guantanamo Bay, the dispatch of a senior Middle East envoy, the unveiling of a new green agenda, the removal of the abortion bar on foreign aid programmes, an eye-wateringly large fiscal stimulus package, major moves to increase government transparency, and now, as was reported on Thursday, a decisive change of approach towards revolutionary Iran.

As each new move is revealed it is hard not to luxuriate vicariously in the self-confident deployment of smart power by a progressive leader at the peak of his influence. But hard not to reflect too — unhistorically, of course, — on the terrible wasted years. How different our globe might have been today if this sort of world view rather than George Bush`s had held sway in Washington since 2001. Yet this moment of potency is simultaneously a moment of fragility. For although America`s government has changed decisively this month, America`s actual power in the world has not. The Republican defeat in November marked the historic failure of the unipolar post-Cold War approach to world power that lasted from 1989 until now. Obama cannot, therefore, be a unipolar president even if he wants to be.

In fact, every international move he makes marks an implicit accommodation to multipolarity, albeit one in which America remains the decisive power. We should welcome this. Yet it follows that Obama cannot be expected to solve the problems of the world on his own. To paraphrase John Kennedy, the remainder of us need to ask what the rest of the world can do for America, not the other way around. And that irresistibly poses the question of whether we in Britain are spectators or players in such a process. It compels us to ask what our own best role should be in contributing to this new order of things.

Inescapably that raises the question of Britain`s relationship with the European Union. Flawed though it is, weakened though it may be, and problematic though it undoubtedly remains, the EU is nevertheless at the heart of any serious strategic answer to the question of how Britain can play an effective part in the multipolar world that Obama is obliged to try to shape.

If he seeks an effective global partner for his efforts on Iran, the Middle East, climate change or the restructuring of financial institutions, he will not look first to Britain — whatever the Downing Street spin machine would have us believe. He will look to the EU, of which Britain is a part. Likewise, if and when China or Russia want to strike deals on trade, energy or almost any other subject, they too will look first to Washington and then to Brussels, not to London.

The debate about Europe in the UK always takes place on the basis that the EU is too strong. Yet the reality is in many ways the opposite. Actually Europe is often too weak, in terms both of the hard power of integrated military effectiveness and the soft power of international influence building. Whatever Europe`s strength vis-à-vis the sovereign states that make up the union, it is certainly too weak to be really effective in representing its own best interests internationally, or in commanding resources that would enable it to sit at the top table as a truly effective player. Britain ought therefore to have a strong national interest in building up the EU.

In order to achieve what? Climate change or overseas aid are often cited as the kind of subjects in which Britain`s interests are most effectively advanced in global forums by the weight of the EU. Rightly so. But what about an even more anguishing and urgent subject, like the hundreds of thousands who are unable to live safe lives in sub-Saharan Africa due to the breakdown of order?

If you want peace in Sudan or Congo or Somalia, you have to want not just international aid but international peacekeeping. Existing peacekeeping efforts, though large and expensive, are also ineffective. Western engagement in these efforts would be controversial, but it could be very effective. Yet it will only happen — to the extent it happens at all — through the EU, not through nation states. There is a pressing need for an intelligent post-Iraq debate about how Europe can best develop, organise and use hard power.

At a seminar in London this week, several senior Labour heavy hitters argued that now, with Obama reaching out to the world, is exactly the time for the European case to be made more urgently in Britain. Labour should press more boldly for merged defence capabilities, then for a Europe-US framework for financial service reform, and for individual European nations to have fewer votes in a reorganised system of global financial institutions.

Fine. But here`s the rub. It is not going to happen. If an instinctively pro-European leader like Tony Blair could not change the terms of Britain`s debate about Europe when he was on the crest of a wave during the late 1990s, an instinctively Eurosceptic leader like Gordon Brown — who was a large part of the reason Blair never turned the issue around — is not even going to try doing so when he is being battered in the polls a decade later. As potential Tory PM, David Cameron would certainly have no intention of going there either.

— The Guardian, London