One of the classic storylines of science fiction is the emergence of a mutant child, with powers far beyond those of adults and no understanding of their use. The theme is carried to its the extreme in Jerome Bixby’s story It’s a Good Life, where the omnipotent mutant is a toddler with no grasp of consequences. With Donald Trump in the White House, the whole world can get a taste of this capricious blundering. That he speculated about buying Greenland is not in itself remarkable: a very large and strategically important island with reserves of valuable minerals is the kind of place in which all great powers will take an interest. As far back as 1946, President Truman offered war-ravaged Denmark a sum in gold equivalent to a billion of today’s dollars for the island – and was promptly rebuffed. Truman did, however, secure an airbase at Thule, which is important to this day for the missile defence systems of the US. He did not, as Mr Trump has done, cancel a visit to Denmark in a fit of pique. That, as the Swedish former prime minister Carl Bildt tweeted, was “well beyond the absurd: Trump [has made] a state visit to a long standing ally dependent on that country being ready to give up parts of its territory.”

Mr Truman, and all the presidents who followed him until 2016, understood that nations other than the US had their own pride and even their own sovereignty. Mr Trump combines a belief that everything ought to be for sale to him with an inability to understand what it might be worth to anyone else. That helps to explain his numerous bankruptcies and later failures as a diplomat.

If the problem with his desire for Greenland were simply his childish greed and lack of self-restraint, that would be serious enough. The watching world has by now factored his personality into its assessments of US foreign policy. What is of lasting concern is the more widely spread attitude to the world’s problems that makes the purchase of Greenland look like a clever idea to anyone in the face of climate change. Greenland is important to the whole world, not just the superpowers, at the moment. This is because its ice sheet, miles thick in parts, is melting at historically unprecedented rates. That’s one of the central mechanisms of our climate crisis, and all that some Republicans can see is that this might expose still more reserves of fossil fuel to burn, and so to accelerate the catastrophe. Mike Pompeo, Mr Trump’s secretary of state, said earlier this year that “The Arctic is at the forefront of opportunity and abundance ... it houses 13% of the world’s undiscovered oil, 30% of its undiscovered gas, an abundance of uranium, rare earth minerals, gold, diamonds, and millions of square miles of untapped resources.”

This is an attitude even more reckless and shortsighted than establishing nuclear bases around the world. Although a nuclear war would wipe out civilisation, there was a logic to nuclear deterrence, which could be argued to have made such a war less likely overall. There is no logic but a toddler’s greed to the unbridled consumption of the Earth’s resources. As the seriousness of the climate crisis becomes more and more obvious, so does the fact that it can only be solved by coordinated international action, while competing nationalisms can only exacerbate it and make the easily foreseeable end worse for all the competitors. A rules-based international order is the counsel of enlightened self-interest, not idealism. But today the most powerful nation on earth is in the hands of a man who can recognise neither his own nor anyone else’s legitimate self-interest.