Keir Starmer’s unraveling is easy to cast as the downfall of a prime minister who blew a commanding majority. After all, only 22 months ago, Mr Starmer secured 411 seats — Labour’s third-strongest performance ever, and its best since Tony Blair’s second landslide in 2001. By that measure, the case for a squandered majority looks straightforward enough. Yet for all its size, Mr Starmer’s majority never amounted to a sweeping public mandate. Labour won fewer votes overall than Jeremy Corbyn managed in both of his general…