What caused the collapse? Voters told Labour candidates on the doorstep that Corbyn was the deal-breaker, and they also cited Brexit. Many white working-class voters in Labour heartlands were old-school patriots who had voted to leave the E.U., and had severe worries about mass immigration. They saw the Labour Party’s waffling and incoherence and delaying tactics on the question maddening, and they hated the PC bromides of the London elite. And though they liked Corbyn’s policies, they were skeptical about how he would ever pay for them. Meanwhile, the Tories under Johnson shrewdly moved left on economics, abandoning austerity, and promising big increases in domestic spending. So vast swathes of Labour seats went Tory — often for the first time in modern history.

We’d be foolish not to weigh this as a possible Bernie scenario. Left populism has real support out there, but a party leader’s credibility as a future national leader is also crucial. The Tories and their press hammered Corbyn on extremist moments in his past: inviting members of the IRA into the Commons, placing a wreath at a ceremony where Black September terrorists were honored, calling Hamas leaders his friends, and several incidents which revealed either Corbyn’s anti-Semitism or his staggering indifference to it in his own ranks.