Britain heads to the polls Thursday, and talk about another election gamble that hasn’t paid off. In the same way President Biden hoped Americans wouldn’t notice his age and Emmanuel Macron assumed the French would rebuff the insurgent right, Prime Minister Rishi Sunak thought—wrongly—that a summer election would focus voters on his virtues. In the event, voters still are trying to figure out what those virtues are supposed to be. Opinion polls have tightened a bit, but the situation remains much as it’s been for most of the past 18 months with the center-left Labour Party running some 20 percentage...