Under Tony Blair, Jeremy Corbyn was a tolerated and ignored backbencher. Today, he is denied even that freedom. And yet his followers have behind them the force of a simple argument. The Labour Party’s last year and a half is a familiar episode in the long decline of social democracy, in which leaders demobilise their supporters and see their vote shrink. But as recently as four years ago Labour was able to increase its support faster than at any time since 1945. Many of Corbyn’s supporters are young, black or Muslim, and these are social constituencies in which the Labour Party is now losing support sharply. If Labour wants to appeal again to those voters, it will need to make some sort of compromise with Corbyn.