It wasn’t supposed to be like this. Fortified by a 20-point lead in the opinion polls, Theresa May, the prime minister of the United Kingdom, called a general election in April assuming that, all things being equal, she couldn’t possibly lose. In 2015, David Cameron had won a small and fragile majority in the House of Commons, but this was Mrs. May’s opportunity to transform it into, as she said, a “strong and stable” government that would be well-placed to lead the U.K. through the choppy waters of leaving the European Union. An increased majority, she promised, would “strengthen” her hand in the forthcoming Brexit negotiations.