2020 was never going to be a good year. A veritable armoury of Damocles swords hangs over us – Brexit, Ukraine, impeachment, tariffs, the cohesion of the Western Alliance, US presidential elections and, of course, that perennial headache, the Middle East.

Donald Trump’s killing of General Qassem Soleimani almost completely severed the threat suspending the Middle Eastern sword. Frantic efforts are being made to retreat from disaster. Hopefully they will be successful, but serious damage has already been done and governments around the world are reassessing their positions in light of the New Year developments.

At the heart of the issue is President Trump’s decision to act unilaterally. He did not consult with Congress or any of his NATO allies before despatching a drone to take out the second most powerful person in the Iranian regime. He claimed that Soleimani was in Baghdad to coordinate a major attack on American forces, but so far no administration official has provided any proof that such was the case.

Trump did what he wanted to do for whatever reasons he wanted to do them and then insisted that everyone – allies, democrats, et al – simply fall into line and support him. It is inconsequential to Trump that the killing of Soleimani is quite likely a breach of international law as well as a blatantly transparent attempt improve his re-election bid and distract the public’s attention from the impeachment process.

This unilateralism is a serious threat to the Western Alliance. Much more than any American demand that European members increase their defence spending to a minimum of two percent of GDP. It is a threat because it undermines the 1949 NATO Treaty which is the centrepiece of European and American security which in turn is the key pillar of international security.

Most people when they think of the NATO Treaty think of Article Five or the “Three Musketeers” clause which says an attack on one member of NATO is an attack on all and commits the signatories to come to the defence of whoever has been attacked. The problem is that Article Five is not a stand-alone commitment. It is part of a wider agreement of 14 clauses, and, like most treaties, governments cannot cherry pick the bits of treaties that they like and ignore the rest.

Article One, for instance, commits NATO signatories to “undertake… to settle any international disputes in which they may be involved by peaceful means….” Possibly more relevant is Article 4 which says members “will consult together whenever, in the opinion of any of them, the territorial integrity or political independence of any of the Parties is threatened.”

It can be argued that Donald Trump did not seek to resolve his problems with Iran by “peaceful means”. He certainly did not consult with his allies. His failure to do so has provided a get-out option for his allies should the Iran crisis continue to escalate. The question is: Would the Europeans want to take it. The answer is likely to be that some will and some won’t.

Britain’s Prime Minister Boris Johnson will almost certainly ignore public opinion and use his 86-seat Commons majority to back Trump in order to secure the best possible US-UK trade deal and preserve the remnants of the Special Relationship. His argument will be that British involvement would act as a brake on a thin-skinned, unpredictable shoot-from-the-hip Donald Trump. The East Europeans who rely on America for protection against the Russian bear will almost certainly fall into line. French President Emmanuel Macron underlined “full solidarity” to protect Western forces in Iraq from Iranian attacks, not exactly a full-throated endorsement, but close. German Foreign Minister Heido Maas was worryingly even-handed, blaming Iran for the general escalation but also criticising the US drone attack. EU Foreign Affairs commissioner Joseph Borrell has invited his Iranian counterpart Mohammad Javad Zarif to Brussels for talks and Commission President Ursula van der Leyden raised eyebrows and Washington hackles when she took three days to comment.

“The problem is,” explained one European diplomat, “we just don’t know how to deal with this aggressive American unilateralism.”

* Tom Arms is foreign editor of Liberal Democrat Voice and author of “The Encyclopaedia of the Cold War” and “America Made in Britain". To subscribe to his email alerts on world affairs click here.