This Nato summit will be defined by one question: how to deal with Donald Trump

Boris Johnson does not yet appear to have abandoned the notion that he can fix Trump with the right words, in the right tone, at the right moment.

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He's making a list and checking it twice, gonna find who's been spending less than 2 per cent of GDP on defence...Donald Trump is coming to town! The president of the United States is among the leaders visiting the United Kingdom for Nato's 70th-anniversary summit.

The big, unspoken agenda item is: what happens to Nato when the commitment of the United States to Article Five – that an attack on one Nato member is an attack against all – is up for grabs? Donald Trump's betrayal of the Kurds shows you just how much consideration he will show to his allies, no matter how many times they might roll out their head of state for tea and cake.

And it's not just Trump who is putting Nato's future in doubt. Recep Tayyip Erdoğan has kicked off the summit by vetoing a plan to defend Estonia, Latvia, Lithuania, and Poland from potential Russian aggression, saying that Turkey will veto any such plans unless their fellow member states recognise that the Syrian Democratic Forces, the majority Kurdish militias that the Turkish army is fighting against in north-east Syria, are a terrorist organisation.

That's the backdrop that led Emmanuel Macron to tell the Economist that “we are currently experiencing is the brain death of NATO”, the solution is for the European Union to take responsibility for defending its own theatre through greater defence integration at a European level – or, in Vote Leave speak, an EU army.

But the problem with that approach is that in reality, for European self-defence to be meaningful without American involvement, what you need is Anglo-French defence integration. One of the ironies of this point in British political history is while the Conservative Party has been mired in arguments about getting out of Europe and a looming European army, the Conservative government has overseen an era of unparalleled defence with France: a journey towards a European army more meaningful and important than any number of airy-fairy statements the European Commission might produce. The tie-up has any number of benefits for both countries, whose shared strategic interests are well-served through close defence co-operation. But to go to the next level, Macron's plans bet heavily that freed from their psychodrama about the words “European Union”, the British Conservatives will be willing to take their close security relationship with France to its logical conclusion. Some Conservative thinkers, including those with a deep and longlasting commitment to Brexit, are of the view that the solution is something like that – a loose trading agreement with the European Union, and a deep security partnership.

But can they get their party there? In common with their centre-right colleagues across the democratic world, under Theresa May, the Conservatives appeared to believe that the right combination of words, spoken in the right tone at the right moment will turn Donald Trump into Dwight Eisenhower. In a decision that symbolised the foreign and European failures of her whole premiership, she dropped everything to visit Trump's White House shortly after his inauguration and declined to address the Dáil, an honour rarely extended by Irish politicians to the British. She failed to secure meaningful political support from Trump on any issue and her Brexit strategy foundered on the question of the Irish border.

Boris Johnson has pursued a more intelligent course. He's used his foreign summits effectively to reiterate to the United Kingdom's allies, particularly in the European Union, that, despite Brexit, he and they remain aligned on the other geopolitical questions of the day, particularly on the all-important Iran nuclear deal and Trump's tendency to start trade wars. His bilateral summit with Leo Varadkar, which focussed on their mutual and shared strategic interests around the Irish border, allowed him to finesse the abandonment of his previous commitment to Northern Ireland's unionists as if it were a diplomatic achievement and not solely a retreat.

But – in common with many of his international colleagues – Johnson does not yet appear to have fully abandoned the notion that he can fix Trump with the right words, in the right tone, at the right moment. Indeed, his pitch to his European counterparts, that he shares their interests on trade and the Iran deal, is based on the conceit that together they can move Trump on these matters: the evidence that they can is, so far, slim.

And that leaves them with the question that will define this Nato summit: should they treat the Trump era as a brief and dangerous aberration before a Democrat defeats him in 2020, or a traditional Republican replaces him in 2024? Or is it, as Macron believes, a sign that Europe has to permanently alter and step up its own ability to defend itself in the 21st century? The United Kingdom's present government doesn't appear to know and the political debate around the looming election hasn't got near to it either.

Stephen Bush is political editor of the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to domestic and global politics.