With the exception of Hungary’s Viktor Orbán and Slovakia’s Robert Fico, it’s safe to assume that Europe is petrified about the prospects of a second Donald Trump presidency. As one European foreign policy analyst told the New York Times last summer: ‘It’s slightly terrifying, it’s fair to say.’

The terror meter went up a few notches this weekend, when Trump addressed supporters at a campaign rally and told a story (who knows if the story was actually true) about the time he told a European bigwig that the United States would protect a European country from Russian invasion if it failed to meet Nato’s defence spending benchmark. ‘In...