Jeremy Corbyn couldn't have won without Labour changing its leadership election rules in 2014, but which more importantly got rid of the electoral college that had given MPs a third of the say over who leads the party. That's why Diane Abbott came last when she ran for leader in 2010, even though in the absolute number of votes she came third out of five. It's one of those wonderful historical ironies that the change to the rules was a victory for the Labour right, the result of a push back against the unions who had been asserting themselves more forcefully within the party.