The rise in support of independence in in spite of the SNP rather than because of it. It is far wider than party political now, with many Labour, Green And fringe socialist group supporters in favour. It is the fault line in Scottish politics.
Another factor is demographic shift. Older voters are of course dying and they are the least likely to change their view, having been told all their life by the full apparatus of the British state that Scotland Can’t. I don’t say that to be provocative, it’s a genuine consideration.
At the same time you have younger voters coming through for whom the concept of independence is the norm and something that old folks were against. That helps.
But the biggest shift is in the Scottish middle classes who look with horror and embarrassment on UK governance. I know a lot of people who were bitterly opposed in 2014 who are now vociferously in favour. They feel betrayed and the promises made to them were disregarded.
It’s a soup of unionists own making. They could have been much nicer and more conciliatory after their victory in 2014, and promises could have been kept. Scotland could have had a special arrangement with the EU after Brexit but all suggestions from Scotland were ignored and sneered at.
Now, regardless of what the SNP do, support will continue to rise. And even a campaign forensically targettongbthe weaknesses on the Yes case, of which there are many, will not be enough.