Barack Obama's promise yesterday to pursue a “tough and smart” new national security strategy that would focus not just on Baghdad but also on Kandahar and Karachi, Tokyo, London, Beijing and Berlin is a message aimed as much at America's allies overseas as it is to voters at home.

The Democratic contender is using a forthcoming trip to Europe, Iraq and Afghanistan, and a foreign policy speech in Washington yesterday, to bolster his credentials as a future commander-in-chief - one area where John McCain has a significant poll advantage. Equally, Mr Obama wants to impress on allies naively hoping for a radical shift in US policy that he will pursue American national interests as single-mindedly as anyone. What the world expects from a Democrat in the White House may prove very different from what it gets.

The focus of both his speech and his trip is Iraq. This is one area of foreign policy where the two candidates have sharply differing views. Mr McCain has never retracted his vigorous support for the war, his backing for the surge or commitment to keep US troops there as long as they are needed. Mr Obama, by contrast, has made much of his opposition, from the start, to the invasion and his determination to bring US troops home as soon as possible. While Iraq was going badly, his denunciations played well with the electorate. Now things are improving, US voters are less gloomy about Iraq. And Mr Obama is finding that he needs a more nuanced message.

Yesterday he insisted that he had not retreated from his 16-month timetable for withdrawal. And he tried to turn the Iraqi Government's insistence on a new military agreement to his advantage. He said that there would be no “precipitous” retreat and conceded that a residual force could remain in Iraq to perform “limited missions”. But, confronting critics who suggest that his Iraq strategy implies a cut-and-run attitude, he challenged the Republicans on both the reason for the war and its fallout. Iraq, he said, had nothing to do with 9/11. It had instead diminished America's security, its standing in the world, its military, economy and the resources needed to confront other global challenges.

By contrast, he insisted, the US should assert itself more vigorously in areas where its interests really were threatened: in Afghanistan and Pakistan; in confronting Iran and rogue states; halting the spread of nuclear weapons; and in protecting the US economy and jobs,

Polls show that Americans are evenly divided on Iraq. Any Democrat, however, has to work harder on foreign policy and talk tougher than a Republican. Mr Obama spoke yesterday of the need to rebuild relations with US allies. But, if he wins, the allies may find him no easy partner. On trade, he will be more protectionist. On US energy security, he will use commercial advantage ruthlessly. And on climate change, he will prove as hard-headed as the Republicans.

On his forthcoming trip he will tell Europeans, Afghans and Iraqis that this Democrat intends to be no less assertive than Mr McCain. Mr Obama has inspired an extraordinary following around the globe. International hopes, though, have run ahead of America's expectations of its would-be commander-in-chief. Mr Obama knows that the “leader of the free world” answers to US voters. Obamaniacs abroad should take note.