There's also the problem of a precedent being set for Scottish independence: if the Leave vote of 2016 doesn't actually lead to Britain leaving the European Union because it's overturned by a second referendum before the result is implemented, why couldn't unionists attempt the same stunt after a future Yes vote in Scotland? However, as I pointed out to Labour MP Paul Sweeney recently, the precedent can't be set simply by SNP support for a referendum - it can only be set if a referendum is actually held, and it probably won't be, partly because of Labour's own stance. And there's the rub: the logic of the SNP's new strategy surely hinges entirely on the assumption that they are supporting something that will never come to pass. Which is fine, and probably justified, but it's a bit of a high-wire act all the same.
Peter Curran asked on Twitter recently what would happen to the plans for an indyref if the SNP's best efforts succeeded, and Britain remained in the EU, or there was an extremely soft Brexit. And the answer can only be that an indyref would be off the table at that point, because there would be no chance of success - Remain supporters in Scotland would breathe the biggest sigh of relief on record, look back on the chaos of the last two years, and refuse to countenance any constitutional upheaval (such as independence) for many, many years to come. But if a Hard Brexit actually happens, the opposite applies - independence in Europe will start to look like the antidote to the chaos.
During the 2016 EU referendum, the SNP leadership were often accused of secretly wanting a Leave vote to further the cause of independence. That was almost certainly an unjust charge - my impression is that they genuinely wanted the peace and quiet of a Remain vote, and would afterwards have looked to build towards an indyref at some point in the 2021-26 parliament. But once the Leave vote happened, it's probably fair to say that any potential overturning of that result started to look inconsistent with keeping the flame of independence burning bright. So, on paper, the SNP are now campaigning for something that is the polar opposite of being in their own best interests.
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