Thanks to Donald Trump, the job has got a whole lot harder. The basic tenets of British foreign policy have been shattered. Yet many of the problems predate him and are self-inflicted. Brexit stares diplomats in the face every day, requiring rictus smiles when reminded of the decade-old decision. Its consequences are not just the obvious ones. One is the informal exchange of ideas and experience that occurred at various EU gatherings; now Brits must knock on the door.