It was Jeremy Corbyn/Momentum who lost it for Labour.
Ultimately this result will be good for Labour - if they ditch the would-be Marxist element and return to the centre left with a credible, electable leader.
But I see that many of them are blaming it all on Brexit. And look at JC's stance on that - his backside firmly glued to the fence all along, presumably not because he didn't truly know his own mind, but because he wasn't sure which stance would win more Labour votes.
He has always reminded me of the student activists who stood outside the student union building every lunchtime when I was a student in the late 60s, handing out Marxist Society leaflets and trying to flog The Socialist Worker.