Photo by Anthony Devlin/Getty Images The truth of the matter is this: unless Keir Starmer steps down, the field of credible contenders to replace him will remain far smaller than the number of people interested in the job. Despite the Prime Minister’s historic unpopularity with the public, he is still more popular with the party faithful – at the last count – than most of his challengers. Anyone coming for the crown would need the backing of 81 Labour MPs to secure a place on the ballot. While there are certainly more than enough MPs who now want Starmer either to go immediately or to announce a timetable for departure, there is no guarantee that 81 or more would unite behind a single candidate. When – or if – that challenger emerges, they will then face Labour’s rank and file, who, as we learned a decade ago, are often a very different kettle of fish from their colleagues in the Commons.…