United States President Donald Trump ruffled his Nato allies by accusing them of owing money to the alliance and to the US. Trump seemed unaware that Nato members’ contributions are voluntary and the target of 2 per cent of gross domestic product (GDP) on defence spending is just a guide.

It is true that many Nato members have not met this target, but no money is ‘owed’ to the US and Trump’s wild accusation has left his allies deeply concerned that the American president does not understand the underlying structure of the western alliance.

Trump used the Nato meeting to increase the pressure on Nato members by saying that the 2014 agreement made at a summit in Wales was a “bare minimum”, and “even 2 per cent of GDP is insufficient for confronting today’s very real and very vicious threats”.

The unfortunate Nato Secretary-General, Jens Stoltenberg, tried to paper over the differences between Nato’s largest member and its shocked allies. He chose not to confront the US president, but instead claimed that Trump had been “clear on his commitment to Nato” and even if he had been “blunt”, he had offered “a very plain and clear message on the expectations” of the Nato allies. In another unexpected twist, Trump called for Nato to include limiting immigration as one of its tasks, although as a military alliance, Nato has had nothing to do with such a task and offers very little expertise in that area.

Trump also failed to remedy his previous comments, which challenged his administration’s commitment to Nato’s Article Five, which defines the alliance’s mutual security guarantees. While campaigning for the US presidential election last year, Trump had said that the US would have to think about coming to the defence of a member-state that was attacked if that state had not paid what he thought was its fair share. This attack on the key understanding of the alliance, which requires that an attack on one state is to be considered an attack on them all, and Trump’s failure to comment on Article Five, left his allies worried.

This failure has a particular relevance for the Baltic states on Russia’s border, which fear Moscow may try a repeat of its 2014 annexation of Ukraine’s Crimea. Their fears were slightly allayed by Polish-born European Council President Donald Tusk who said after meeting Trump that even if he was “not sure that we have a common position on Russia”, on the conflict with Ukraine “we were on the same line”.