Corbyn persistently refused to answer the unreasonable question about whether he would campaign for remain or leave in a second referendum campaign. That looked weak, but in fact his stance is responsible and honest. In the (unlikely) event of his obtaining a working majority, he has promised to negotiate a new deal with the EU. He doesn't know whether the EU will negotiate one at all (meaning he could well be stuck with Johnson's), or would give the process enough time, or whether they will be inclined to negotiate for a much softer brexit than Johnson managed (I suspect that they would, especially if Corbyn asks for a customs union and closer alignment with the single market). The EU could well cut up rough over free movement. All sorts of things. So who knows what a deal would look like? Which is why the question is unreasonable.

And there are faint echoes here of Cameron calling a referendum then campaigning for it to "fail"...