Only a year ago, many feared that Donald Trump’s dealings with Kim Jong-un might end with a bang. Then came the Singapore summit. Mr Trump boasted that they “fell in love” and that North Korea was no longer a nuclear threat. The bromance did not look sustainable. Now a follow-up in Hanoi has ended in a whimper, collapsing without the heralded signing of at least a limited deal.

North Korea needs an easing of sanctions and wants to pursue economic development; Mr Trump wants a diplomatic triumph with his name emblazoned on it. But these powerful drivers are not enough to bridge the gulf between the sides. While North Korea speaks of denuclearisation on the peninsula, it has no intention of unilateral disarmament – as US intelligence officials note. Gestures such as halting missile tests have some value, in real terms as well as in building the relationship, and disabling the Yongbyon nuclear plant would have more; the question is how much they are worth. Many had feared Mr Trump might pay too highly, as he did in Singapore.

Hours before their talks in Hanoi, he predicted a “fantastic success” in their long-term dealings. His hunger for a personal triumph was spurred by the excoriating testimony from his former lawyer Michael Cohen back home. When it all went wrong, he said the US had walked because Mr Kim wanted all sanctions lifted – a huge step, not in his gift. North Korea insists it sought only partial (though substantial) sanction relief. It had also made it clear prior to talks that it wanted to see sanctions lifted before it put Yongbyon out of action. The reported sidelining of Steve Biegun, the US special representative, cannot have helped – but may have been effect as much as cause. Many already suspected John Bolton was key to the talks’ collapse.

The question is where they go from here. In his post-summit press conference Mr Trump boasted of progress, described their dealings as “very friendly”, and even exculpated Mr Kim over the treatment of Otto Warmbier, the US student who died after being held in North Korea for 17 months. North Korea struck a harsher tone, saying Mr Kim “got the feeling that he didn’t understand the way Americans calculate” and may have “lost the will” for further talks.

The risks of another summit are now much greater for both sides, and its appeal diminished. Mr Kim has already been boosted at home and abroad by two presidential meetings. His train home runs through China, and it now seems even likelier that he will stop off in Beijing. Mr Trump’s warm embrace pushed China into hugging the North close, despite its previous distaste for Mr Kim. South Korea got talks back on track after Washington and Pyongyang hit problems before. But it will find it harder going this time, and until those relationships improve, it cannot get much further with the inter-Korean economic initiatives it wants to pursue.

It may be that talks simply peter out, with the US essentially returning to Barack Obama’s “strategic patience”. It was a poor idea the first time round, and Pyongyang’s weapons programme is now much further advanced. But the fractious response North Korea gave last night suggests that worse outcomes are possible. Yes, the world is safer than when Mr Trump and Mr Kim were trading insults. But Mr Trump’s vanity diplomacy has strengthened the North Korean leader. A humbler, more careful and more pragmatic approach, seeking to freeze rather than eradicate the weapons programme, would have been a far wiser course.