Embedded deep in the rationale of the security relationship between the US and its European and Nato allies is the idea that the best guarantee of their collective security, big and small state alike, lies in an "unshakeable" treaty-based commitment to stand together as one, collective defence: Nato's Article 5. An attack on one is an attack on all.
But it's a concept whose implications, and essential requirement of mutual trust, Donald Trump does not seem to understand or embrace fully. His "my-country-right-or-wrong" insistence that allies stand unquestioningly behind the US, not least in the wake of the killing of Iranian general Qassem Suleimani, may well fatally undermine what many see as a cornerstone of the western alliance, a glue binding it together.
His attitude to Nato commitments – quite apart from his persistent berating over member-state financial contributions – has alarmed many of his allies who were particularly shocked by an interview he gave on Fox News back in July 2018.
A few member states, not least in the Baltic region, are distinctly nervous about the solidity of the Nato doctrine
Asked by a right-wing commentator about Nato's obligation to defend its newest member state, Montenegro – "why should my son go to Montenegro to defend it from attack?" – the US president responded: "I've asked the same question."
He described Montenegrins as a “very strong” and “very aggressive people”. “They may get aggressive, and congratulations, you’re in World War III,” he added in comments that some Europeans may now well be echoing about the US itself in the wake of the Suleimani killing and its potential aftermath.
It was not the first time Trump cast doubt on the Nato doctrine, and although he has since rowed back partially, not a few member states, not least in the Baltic region, are distinctly nervous about the solidity of its guarantees.
Not surprisingly, others in France and Germany have also increasingly spoken of the need for European self-reliance in defence. Within the EU that is reflected in a stronger commitment to building joint defence capabilities.
The Nato treaty Article 5 commitment and obligation to collective defence begins: “The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all...” It requires member states to provide their ally with political and military support.
It has only ever been formally invoked once, on September 12th, 2001, the day after the World Trade Center and Pentagon attacks. But Nato has taken collective defensive measures in other situations, including deploying missiles on the border of Turkey and Syria in 2012.
Allies may share the US president's dislike for Suleimani, but few accept the legality of the attack
Russia’s annexation of Crimea in 2014 and the rise of Islamic State in recent years led the organisation to implement a huge increase in its collective defences, including tripling the size of the Nato Response Force.
Article 5's strength as a tool of security lies in the automatic nature of the guarantee – the certainty that if Russia were to invade Estonia, for example, it would face immediately and unconditionally the military might of the whole alliance. But is it really still automatic?
When Turkey's president Recep Tayyip Erdogan controversially sent troops in to northern Syria to attack western-allied Kurds, Ankara made noises – no more – about expecting Nato allies to back it if its forces came under attack there. No chance. The Turks, who were at the same time encroaching on the territorial waters of another Nato member state, Cyprus, have been precariously stretching the limits of what Nato expects of members.
In launching his deeply destabilising attack on Suleimani, Trump is also pushing boundaries and chipping away at that automaticity. Allies have responded with statements of such qualified support that there is no hiding the deep disquiet in horrified capitals. They may share the US president’s dislike for Suleimani, but few accept the legality of the attack, and all can see the terrible potential for escalation into all-out regional war.
Should Iran retaliate beyond Tuesday night's air strikes in Iraq, the European allies will rally round and provide the US with the political support that it needs even more than military aid. But there will also be an angry sense of betrayed trust, that the US will have brought it on itself through its unilateralist recklessness, and an inevitable questioning of the idea that it can go on demanding unquestioning support.
The Nato relationship will begin to fray.
As for Ireland, unencumbered by any Article 5 obligations, we are free to speak our minds. In theory. But antagonising Washington, whether Trump is in charge or not, is not part of the national playbook.