As ambassadorial jobs go, US diplomats can do worse than being posted to Europe. The residences are huge, and the life is peaceful – at least west of Kyiv. “You’re in friendly territory,” said Daniel Fried, a former US ambassador to Poland. When disputes arise, most can be kept behind closed doors. But recent public spats among three US ambassadors and their respective hosts have given Europe a taste of the Trump administration’s firmer, less hushed approach to diplomacy. To Washington, the dustups are the sort of tough love the continent needs. To Europe, they are needless antagonism which violates...