European leaders behave like supplicants to an almighty Trump. Putin just sees him as a protege | Rafael Behr

Nato's Trump-whispering has been vital for Ukraine - but the White House and the Kremlin have their own special channel

A hungry pigeon given food at frequent but irregular intervals will develop weird rituals - tics, dances, erratic head jerks - in the hope of summoning another morsel. BF Skinner, the psychologist who first demonstrated this effect in 1947, described the birds adopting a sort of superstition ... as if there were a causal relation between its behaviour and the presentation of food, although such a relation is lacking".

It would be unkind to compare that bird-brained affliction to the behaviour of European leaders trying to make sense of Donald Trump's erratic distribution of favours. Their diplomatic manoeuvres are more rational. And they get results. But there is also an element of superstition. Visiting politicians make lavish gestures, strike unusual poses, cultivate White House contacts, looking for the sequence of steps that will unlock a steady supply of American amity. The causal relation is not lacking, but it is unreliable.