With echoes of Presidents Reagan and Kennedy stirring the huge Berlin crowd, Barack Obama yesterday challenged a new generation of Americans and Europeans to tear down the walls separating estranged allies, races and faiths. “The walls between old allies on either side of the Atlantic cannot stand,” he told thousands of cheering Germans, a stone's throw from where the former US presidents had challenged the Soviet Union. The main danger now, he added, was division between the US and its allies.

If Europeans were the electorate in the US presidential contest, Mr Obama would be more than victor. In the popular vote, he would far outstrip the landslides won by Lyndon Johnson and Ronald Reagan. The huge crowds attending Mr Obama yesterday in Berlin are an indication not only of sympathy but of adulation.

Irrespective of the relative merits of the contenders for the presidency, there is an encouraging message here. Europeans are recovering their admiration for America. Part of Mr Obama's appeal reflects his not being President Bush, whose public diplomacy on issues where the US and Europe are at odds has tended to be abrasive even where America has a good case.

But even apart from Mr Obama's personal appeal, European public opinion has been shifting. Polling evidence suggests clear improvement in European attitudes to the US since the transatlantic ructions caused by the Iraq war. Whoever wins in November, the signs from the US are that this love affair is lopsided. What Mr Obama hears on his European trip, therefore, is as important as what he says.

The US is crucial to Europe's wellbeing and security. But in recent years, America's attention has been preoccupied by the intractable conflicts in the Middle East; by the growing economic might and political influence of China; and by the threat of terrorism that has its origins far beyond the borders of America's Nato allies. Europe has no inherent claim to be the central component of US strategic interests.

In an essay in Foreign Affairs magazine last year, Mr Obama emphasised the need to “rebuild our ties to our allies in Europe and Asia and strengthen our partnerships throughout the Americas and Africa”. That is a long list. But Mr Obama himself has until now evinced little European interest. Last December it was reported that he had convened no policy hearings of the Senate Foreign Relations Sub-Committee on European Affairs since becoming its chairman the previous January.

A new partnership is vital if Europe and the US are to negotiate the threats and opportunities beyond their borders. This is more than simply the military or political revival of Nato. In means a new convergence of hopes, values and ideals.

In dealing with immediate threats to our security, such as terrorism and climate change, the US under either candidate for the presidency is likely to exhibit much continuity in policy. Emerging problems will be an increasingly assertive Russia, an unstable Africa, nuclear proliferation in the Middle East, dislocation of the world economy through a glut of Asian savings and the scramble for resources in the Arctic. There are few such challenges that would not benefit from more US influence rather than less. This is a time for a renewed Atlanticism.