One foreign policy achievement that Donald Trump prefers not to boast about is his role in helping Mark Carney win last year’s Canadian general election. The incumbent Liberal party faced crushing defeat before Mr Trump threatened to annex Canada. Mr Carney’s candidacy was buoyed up by a patriotic rally against US bullying.

Perhaps because his country has also been coveted by Mr Trump, Mr Carney has given one of the most clear-sighted responses of any democratic leader to the US president’s designs on Greenland. Addressing the World Economic Forum in Davos this week, the Canadian prime minister set out the challenge for countries whose security and prosperity have depended on a global system underwritten by the US.

“The rules-based order is fading,” Mr Carney said, making way for a time of “great-power rivalry”. The change compels “middle powers”, such as Canada, to build new coalitions, invest in security and diversify economic ties. A new multilateral framework must be made from the ruins of the one Mr Trump is vandalising.

Britain is also a middle power, and one whose position is uniquely awkward as the US, its closest military partner, is provoking a tariff war with its closest trading partner, the European Union. Sir Keir Starmer has cultivated good relations with Mr Trump while aligning the UK economy more closely with the EU as part of a post-Brexit “reset”.

Supporters of the prime minister’s approach cite the need to prevent the US completely abandoning Ukraine to Russian aggression. Performative denunciation of the president might achieve little except to make Nato less popular in the White House and jeopardise Kyiv’s position in ceasefire negotiations.

Earlier this week, when threatened with punitive US tariffs for supporting Danish sovereignty over Greenland, Sir Keir extolled the merit of “calm discussion” to resolve the issue. The US president repaid Sir Keir’s measured tone with aggression, attacking his plan to transfer the Chagos Islands to Mauritius as “stupidity” (although that arrangement previously had White House approval). The prime minister rightly pushed back, telling MPs he would not be pressed into changing his position. It should be clear now that the strategy of mid-Atlantic equidistance is unsustainable.

Mr Trump’s contempt for old US alliances goes to the core of his politics. Mr Carney may be premature when he says the rupture from the old order has already happened, but it is imminent. Gordon Brown made the same point in the Guardian earlier this week, calling for a “coalition of the willing” to “build a new global framework”.

Sir Keir doesn’t express himself in such terms. He focuses on practical problem-solving in the moment, which he says is the way to achieve results. He is testing the limit of that approach. Without an account of the big picture, the prime minister will not get public consent for the difficult choices that face the UK. One of the tasks incumbent on middle powers, in Mr Carney’s analysis, is to “name reality” – not indulging a pretence that the old ways can endure.

Sir Keir has proved he is adept at diplomacy, but he is a political leader, not just a diplomat. His duty is not only to work behind the scenes but to be candid with the public and “name the reality” of the epoch-defining global crisis that Britain must now navigate.