Whether it’s Trump or Harris in office, Starmer will need an incredible US ambassador. Here’s my vote | Martin Kettle

The widening of the Middle East war has a multiplicity of woeful causes and grim consequences. Many have the potential to become even more intractable in the weeks to come. Fresh human suffering in Israel, Lebanon and beyond is only the start of it. Donald Trump is wrong to claim we are on the brink of a third world war. But these events have global implications. Remember what happened after 9/11.

The latest bombings and missile attacks mark a historic failure for politics and diplomacy. This is not the first such failure in the Middle East. But wishing that diplomacy could prevail will not make it happen, and even fragile ceasefires are a long way off right now. As angry populations rally behind the respective combatants the prospects for desperately needed political solutions are almost negligible. You can't stop a war if those on all sides are determined to fight.

On the global scale, the implications for Britain and for Keir Starmer's government come a long way down the list of the escalation's most important consequences. In domestic terms, however, they still matter very much indeed. The Gaza war has already made a powerful impact on British politics. Israel's latest conflict with Iran and its proxies is likely to do the same. The shadow of the Iraq war is a lasting one, more than 20 years on.

Yet Britain is not some touchline observer of events in the Middle East. British listening stations in Cyprus monitor the Middle East 24/7. British jets, based in Cyprus, fly over Syria and Iraq almost daily. Those same British jets flew missions to help protect Israel in April, and did so again this week in response to Iran's missile attacks. Like it or not, Britain also has a history in the region.

All of which underscores the high seriousness of the strategic choices that Starmer faces in foreign policy. Like all European nations, Britain now exists in an unstable world shaped by Chinese power, the threat from Russia, US political uncertainty and climate change. It has expelled itself from the European Union. Starmer was in Brussels today to try to make the best of these volatile realities.

No one should kid themselves that this is not a difficult hand to play. The difficulty lies behind the escapist and trivialising foreign policy solutions in which Boris Johnson and Liz Truss took refuge, in office and afterwards. Starmer's seriousness offers a quite different response to theirs but it brings another sort of danger. It puts him at risk of not challenging some inherited orthodoxies of British foreign policy at a newly unstable time for which they are no longer adequate. Dean Acheson's 1962 comment that Britain had lost an empire but not yet found a role still echoes.

Starmer himself has little background in foreign policy. He gets day-to-day advice from his national security adviser, Tim Barrow, and his foreign policy adviser, Ailsa Terry. It is hard to say from the outside if they are the ideal team for the biggest foreign policy call he faces as prime minister. That call is not, though, over the Middle East war, or the defence of Ukraine. It is not even over the relationship with the EU. It is over the relationship with the US.

British foreign policy always seeks to hug America close. But a month from now, the US reaches a fork in the road. Trump and Kamala Harris offer radically different approaches to the country's global role. These differences will shape Washington's approach to every important global issue - including Ukraine, the Middle East, China, climate, and digital regulation - for the coming four years. They will be reflected, too, in the way the US operates towards international bodies including the United Nations, Nato, the International Monetary Fund and the international criminal court.

The outcome will shape British foreign policy too. A Harris victory would permit something like business as usual. But a Trump win would not. Trying to hug Trump close risks being unsuccessful, dangerous and damaging. Even trying to influence him would require a very special skill set, notably the ability to catch Trump's attention on Fox News. And Harris would be operating in a more volatile world, too, in which constrained US power might not give priority to British and European interests.

That is why, for Starmer, there is an umbilical link between the pressures of a massive event such as the Middle East war and an otherwise relatively niche decision, like who should be the next UK ambassador to the US. Seen through the global lens, the imminent appointment of Karen Pierce's successor in Washington is relatively minor. Seen through the UK lens, however, it is one of the hinges on which the success or failure of Starmer's government will depend.

Unsurprisingly, No 10 has said the Washington job - the special relationship's most special post - will only be allocated after the US election. But it will be a defining moment all the same. Politicians including David Miliband, Catherine Ashton and Peter Mandelson have been mentioned. So have current ambassadors, including Menna Rawlings (now in Paris) and Barbara Woodward (now at the UN). Whitehall veterans such as Tom Scholar (former head of the Treasury) and Vijay Rangarajan (now head of the Electoral Commission) may be in the frame too.

It's a job that Labour, nowadays full of West Wing wannabes, has always taken especially seriously. Peter Jay, who died last month, was appointed to the ambassador's luxurious Massachusetts Avenue residence by his Labour prime ministerial father-in-law, James Callaghan, in 1977. "We want you to get up the arse of the White House and stay there," were the instructions from New Labour in 1997, when the late Christopher Meyer was despatched to be Tony Blair's man in Washington.

The appointment rests very personally with Starmer. He has surely now learned that the global agenda will also determine Labour's future, whether Trump or Harris wins. The appointee therefore needs to be someone with the ear of the president but with the ear of the prime minister as well. That's why, in the end, my prediction is that the job will go to a man who, untypically, did not reply to my inquiries on the subject this week.

A generation ago, as Blair's chief of staff, it was he who gave Meyer those robust instructions. It was also he who played a key role in the hard-won peace process in Northern Ireland. At a time when another peace process is again so urgent, it is hard to think of a stronger candidate than Jonathan Powell.