The close and compelling contest between Hillary Clinton and Barack Obama for the Democratic nomination has perhaps obscured John McCain's achievement in becoming the presumptive Republican presidential candidate. The Arizona senator will be 72 in August and has significantly less money than either of his possible rivals. He is associated with a president whose approval ratings rarely exceed one in three voters and whose country appears to be sinking into recession. Mr McCain also has a reputation for repeatedly telling people things that they often do not want to hear. In theory, this is no basis whatsover for a successful charge to the White House. In practice, he has a very respectable chance of victory, and Britain, like other American allies, should be considering what its policy response should be were he to sit in the Oval Office.

One of the senator's charms is his candour. While other presidential hopefuls might leave a degree of ambiguity in their wake, Mr McCain has been entirely frank in what he told Gordon Brown (and David Cameron). The same theme comes through in his interview with The Times today. He is putting himself forward to be President on the basis of his intense understanding of national security issues. For him, from Day 1, foreign affairs and military matters will be the core of how he sees his task. A McCain administration would seek to complete Iraq's transition to a stable and prosperous democracy, carry the fight to the Taleban in Afghanistan, be exceptionally wary of Iran's nuclear potential and be willing to take on al-Qaeda and other Islamist organisations. If that sounds familiar, the difference lies in his desire for a genuine dialogue with America's allies and a recognition that the US image in the world must be improved.

Much of this would not be difficult for Mr Brown. But Iraq could be a source of contention. Downing Street has left the impression that it would prefer to withdraw all British troops from the south and redeploy them to Afghanistan. There is some military logic to this and also the political incentive for Mr Brown to put some distance between himself and “Blair's war”. Mr McCain, by contrast, does not regard Iraq as “Bush's war” or “Blair's war” but as a challenge critical to the credibility of the Western alliance and the broader struggle for international security. A continued British presence in Iraq, even if more focused on reconstruction and development than active patrols, would, he believes, be of notable value in assisting the Iraqi Government.

This is a message that Mr Brown would be wise to heed. The surge in US troops in Iraq, of which Mr McCain was the earliest public advocate, has allowed for notable progress and gives hope for Iraq's future. It has not, though, ensured the destruction of al-Qaeda, the reconciliation of Shia and Sunni communities or a smooth passage to a benign ultimate outcome. It is work-in-progress and it would be wrong for other nations, particularly Britain, to assume that it can be left to the United States and the Baghdad Government to complete it. Basra is not aching for the British Army to return to its immediate postwar activities. But it does not want to be abandoned either. Mr McCain's message is that Britain should maintain a close interest in Iraq as well as Afghanistan. Whether or not he becomes the 44th President, his assessment is right.