Today brings word of the first full-scale Scottish poll for quite a while, but frustratingly it's from SurveyMonkey - they have little track-record in Scotland and therefore it's very difficult to interpret their results.
Liberal Democrats 4%
The percentage changes that are being reported in some quarters are from the actual 2015 general election result and not from any previous SurveyMonkey poll. We don't know whether SurveyMonkey's methodology is SNP-friendly, Tory-friendly, Labour-friendly or essentially neutral, so it's impossible to say for sure whether 39% is 'bad' for the SNP or whether 29% is 'good' for the Tories. The Sun are attributing epic significance to the fact that the SNP are below 40%, but in reality 39% is within the standard margin of error of the 41-42% recorded by the SNP in the two YouGov polls in the campaign so far. A 10% gap between SNP and Tory is the lowest reported by any firm during the campaign, but not by much - Panelbase had the gap at 11%, and nobody (with the arguable exception of Google surveys) has had it higher than 15%. So we'd be jumping to enormous conclusions if we assume that this single poll is proof that the SNP's position has worsened over the course of the campaign - it's perfectly possible that SurveyMonkey's methodology would have produced similar results (at least in respect of the SNP-Tory battle) a month ago.
Nevertheless, there are a few possible causes for concern here -
* The poll reinforces the impression that there has been a Labour recovery, and opens up the possibility that the extra votes are coming more from the SNP than the Tories. If that is indeed what's happening, it's a tragedy twice over. Voters moving from SNP to Labour are just making it more likely that the Tories will win several seats in Scotland, and thus potentially boosting Theresa May's overall majority. In the vast majority of the Tories' target seats in Scotland, the SNP are the only party that can stop them.
* For what it's worth, SurveyMonkey's numbers are eerily similar to today's Scottish subsample from YouGov, which says : SNP 40%, Conservatives 30%, Labour 25%, Liberal Democrats 4%. As far as I know, YouGov are the only firm who claim to weight their Scottish subsamples properly (although admittedly the margin of error on such a small sample will still be enormous).
* There's a distinct lack of evidence in any of this that the Tory slump south of the border has been replicated in Scotland. Perhaps that evidence will never arrive - perhaps it simply didn't happen.
* If the SNP's lead over Labour has slipped to 15% or below, we have to accept that some seats may be lost to Labour (although it should be only a handful, unless the situation deteriorates).
My own interpretation is that the SNP are simply suffering from their traditional handicap in Westminster elections - this is an away fixture for them, and they are being largely ignored by the London broadcast media which unfortunately still enjoys such huge influence in Scotland. (2015 was a freakish exception because of the paranoia in London over the Jocks actually having some say within government.) However, the good news is that the SNP are still comfortably in first place, and if they can get their voters out (a vitally important 'if') the first-past-the-post system should convert that into a handsome victory. Even The Sun acknowledge that the SurveyMonkey poll would see the SNP winning more than two-thirds of seats in Scotland. And there are some advantages to this election being increasingly framed as a traditional Tory v Labour battle - it means that in some battleground seats, the SNP will be able to turn the tables on the unionists' favourite tactic by targeting Labour and Lib Dem supporters with the message : "only the SNP can stop the Tories here".