There is a tendency these days to conflate successful diplomacy with garnering favourable headlines. Negotiating powder is rarely kept dry. Keeping an opponent guessing about one’s intentions and capabilities is secondary to issuing punchy soundbites that play well with the media. Politicians, feeling the hand of history on their shoulder, fall victim to grandiosity — until grim reality taps them on the other one. This is now happening to Sir Keir Starmer as he watches his vaunted “coalition of the willing” for a muscular European peacekeeping force in Ukraine evaporate. As reported in this newspaper, appeals from Britain and France...