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It's not clear to me yet whether it's an advantage for Johnson or a disadvantage that it's not actually within his power to guarantee a 31st October exit or not. If the only way out on that date is with a No Deal exit -- and, let's be clear here, the "if" is more or less redundant, unless Johnson accepts piecemeal changes to the existing Withdrawal Agreement -- Parliament will try to block it. Johnson will presumably try to veto that block, and Parliament and the Courts will try block him on that, too. Maybe he can exploit that to force an early election in which he, and the Brexit Party, can (with some justification) claim that we'd be gone if it weren't for those dastardly scoundrels who paid attention to the overwhelming evidence that exiting without the proper arrangements would be hugely damaging. Or maybe not.
I don't think I've ever wanted to be more wrong about anything than about this. If I am right, then the country is on the verge of tearing itself apart, politically and economically. If Johnson et al are right, then he leads us out of the EU, the economic damage is superficial at worst, and the UK successfully demonstrates a new and astonishingly effective approach to international relations.