At the same time, the Greens could well be heading for a record performance and certainly should do well enough to ensure that, irrespective of exactly how well the SNP do, a majority of MSPs will be in favour of holding another referendum, thereby setting up a clash with Boris Johnson in the not-too-distant future.
Yet there is still much about this election that is uncertain – and which matters.
The first and perhaps most important uncertainty is whether the SNP will secure an overall majority on their own or not.
That matters for two reasons. First, if Nicola Sturgeon has a majority she will be able to dictate when and how a second referendum is pursued. She will not be having constantly to look over her shoulder to ensure the Greens are still onside.
Second, it was the SNP’s success in winning an overall majority in 2011 which paved the way for the ballot that was eventually held in September 2014. That election persuaded David Cameron the SNP had won the ‘moral right’ to hold a referendum – and so if the feat were to be repeated this time Boris Johnson will be left with the difficult job of explaining why that precedent should not apply now.
However, while some polls suggest that the SNP might win a majority others have suggested that they could fall short.
This reflects the fact that how many seats the SNP win is likely to depend on how well they do in nine knife-edge constituencies where either the Conservatives or Labour are defending a majority of five points or less. If the SNP were to gain six of these that could well be sufficient to deliver the party an overall majority irrespective of what happens on the list vote.
Those polls that put the national level of SNP support at 48 per cent or more and the Conservatives and Labour on little more than 20 per cent imply that the swing to the nationalists since 2016 will be enough to see at least half a dozen of these crucial marginals fall into their hands. Those that put support for the SNP a little lower and that for the two principal opposition parties a little higher suggest that the SNP will fall short.
However, this is only true if the national swing in the polls is replicated in these crucial seats.
In practice, there is likely to be some variation. For example, given the Conservatives’ heavy dependence on Leave voters, the party may well find it easier to defend Galloway and West Dumfriesshire, where nearly half voted Leave in 2016, than they are Eastwood, where only around one in four voted that way in 2016 – even though on paper the two seats looks equally marginal.
Meanwhile, the personal support accrued through many years of service as the local MSP by John Scott in Ayr and Jackie Baillie in Dumbarton may enable them to withstand the nationalist tide, while, conversely, Ian Gray’s decision to stand down in East Lothian and Ruth Davidson’s in Edinburgh Central could make those seats more difficult to defend.
In some instances, how many voters decide to back whichever party they think is best placed locally to defeat the SNP could also be crucial.
In short, whether or not the SNP secures an overall majority could depend on local considerations in just a handful of constituencies.
If the SNP cannot win 65 constituency seats they might still be able to make up the difference by winning one or two list seats where the party is less dominant, viz the Highlands & islands and the South of Scotland.
But the SNP’s chances of doing so have potentially been diminished because the party is performing less strongly on the list vote – perhaps by as much as ten points or so.
Partly this is the result of the intervention by Alex Salmond’s Alba Party, which is claiming the support of around seven per cent of those who are backing the SNP in the constituencies. This is only enough to deliver Alba around three per cent of the list vote nationally – too little for the party to win anything other than the odd seat – but still enough potentially to undermine the SNP’s chances of winning list seats.
More significant is the challenge being posed by the Greens, who are being backed by around one in eight SNP constituency voters on the list ballot.
There is also a second important battle taking place – this time on the unionist side of the constitutional debate.
Since securing second place at Holyrood in 2016, the Conservatives have been able to portray themselves as the principal voice of unionism north of the border as well as the party that represents the interests of the UK as a whole. They are keen to retain this dual role.
Labour, in contrast, are keen to start to reverse a calamitous decline in the party’s support over the last 20 years.
Although the party appears to be roughly neck and neck with the Conservatives on the constituency vote, most polls suggest that Labour is still well behind on the list vote – which is the vote that will primarily determine how many seats the party wins.
It seems that a significant body of Labour’s constituency support is proposing to back the Conservatives on the list – persuaded perhaps by the Conservatives’ (debatable) claim that a list vote for them is the best way of stopping an SNP majority.
In truth, there is still much left for the parties to fight over in the final hours of the campaign.
John Curtice is professor of politics, Strathclyde University and senior research fellow, ScotCen Social Research