US President Donald Trump sang the praises of King Charles after the latter’s state visit this week. He even lifted some tariffs on Scotch whisky as a favour to the British monarch.

The king delivered a diplomatic masterclass on the trip, mixing praise for his host with subtle criticism. It’s unclear, though, whether it will make a major difference to a transatlantic relationship troubled by divisions over issues including the Iran war.

“In the short term probably yes, in the long term probably...