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If he does stop it before the real panic sets in, leave voters will argue that he undermined Brexit from the start and that the EU would have flinched first if not for him. It would likely stay a divisive issue for a long time.
I don't see a way that this current period ends without there being a split in the Conservative party, with one part welding permanently with UKIP and the other moving more to the centre-right.
If he does stop it before the real panic sets in, leave voters will argue that he undermined Brexit from the start and that the EU would have flinched first if not for him. It would likely stay a divisive issue for a long time.