The news, as broken by the Washington Post, that the Trump Administration threatened to levy a 25% tariff on British car exports to the US unless Britain warned Iran of violations of the Joint Comprehensive Plan of Action, a deal in which Iran would accept strict rules and oversight of its nuclear activity in exchange for being allowed back into the international community, should concern us all.

Of course, it wasn’t just Britain – the French and Germans were threatened too.

But the difference between us and them is that the French and Germans are part of a bigger group, and have leverage too – a sizeable market which can be used to balance American pressure. We, on the other hand, want a trade deal with the Americans. And, of course, you can always make a deal, depending on how desperate you are, and how much you’re willing to give away to get it. It’s equally clear that American foreign policy under Trump is to use trade as a weapon, even in relation to your supposed allies.

It’s at moments like this that a British government realises the limits of sovereignty. We are a nuclear power, but the weapons are supplied by the Americans, and can just as easily be made unavailable going forward. Free trade is only as free as the biggest or most cynical economic powers decide they want it to be – the effective demise of the WTO’s Appellate Body due to the unwillingness of the Trump Administration to agree any new appointment is a sign of just how vulnerable the rules and sanctions are that are designed to protect it.

It would be easy to simply say, “I told you so”, and sit back and wait for things to go sour. But if Boris Johnson and his cabinet are serious about being an internationalist, outward looking economy, they have to start making the case for international institutions and for rules-based engagement. And, as liberals, we need to be explaining why working within the various multilateral organisations that quietly enable the modern world to function is necessary, if only so that the British public might be minded to do so in a European (or wider?) context in the future.

Under Donald Trump, the United States appears to be an ever more unreliable partner, having been a force for good for a century or more. His actions have done more to promote European defence integration than even the Soviet Union did, making a European Army more like a need than a threat. And, in a world where the alliances we trusted in for so long, like NATO, look rather shaky, Britain finds itself stuck between greater powers, looking to distance itself from the trend towards regional blocs.

Sovereignty is a wonderful concept, offering a warm glow to the nationalists, but when the neighbourhood is becoming less safe, what you really need are friends you can rely upon. And who are Britain’s faithful friends now?