The Holyrood elections will be the “most important in Scotland’s history”, according to Nicola Sturgeon. She hopes to repeat the SNP’s 2011 performance and win an overall majority to claim a mandate for a second independence referendum. But the SNP is often coy about that mandate, preferring the more anodyne “choice about the future”, and it surrounds the commitment with caveats designed to reassure voters.

A referendum will only happen after the Covid crisis has passed and a citizens’ assembly has considered “the kind of country we want Scotland to be”. That leaves plenty of wriggle room, and is wide open to interpretation. It allows the SNP to appeal to supporters of independence without scaring away potential SNP voters who have reservations about it. It also gives the SNP some freedom to choose the time to push for a referendum.

The pandemic has also helped the SNP in other ways. Voters have rallied around the saltire, not the union jack, during the crisis. It has created numerous opportunities to highlight Sturgeon’s incumbency as first minister, her communication skills and ability to master a detailed brief, as well as encouraging comparisons with Boris Johnston. Failings in the handling of the pandemic, most obvious in discharging vulnerable elderly people into care homes at considerable cost to life, have had little impact on the SNP’s popularity. The pandemic also shifts the focus away from the Scottish government’s wider record during its time in office.

Oppositions, it is often asserted, don’t win elections but governments lose them. The SNP’s record ought to put it on the defensive. But the party presents itself as being in government and opposition at the same time. It governs in Edinburgh and uses this base to oppose London rule. Blame games are made easier in multi-level systems, and it never takes much to convince many Scots that the Tories in London are to blame for Scotland’s woes. The SNP will always win the battle to be the party most willing to stand up for Scotland against Westminster. Take independence and the pandemic out of the election, and the SNP would be struggling.

At the start of her premiership, Nicola Sturgeon promised to “close the [educational] attainment gap completely”, but the most recent independent evaluation by Audit Scotland concluded that progress had been “limited”, falling short of the government’s aims. Public Health Scotland, launched a year ago, warned that health inequalities had worsened over the previous decade. People living in Scotland’s most deprived areas could expect on average 48.2 years of good health, compared with 72.3 in the least deprived areas. Drug deaths have increased by 160% during the SNP’s time in office.

The Scottish government has siphoned off local government money to try to address such deficiencies, leaving local government to face increasing demands with fewer resources. Local public services have been cut across Scotland, including Sturgeon’s own back yard in Glasgow. The SNP approach to policymaking is reflected in its manifesto, which proposes to sprinkle goodies around, enough to create a headline or appease groups of voters, but not enough to have much impact on outcomes. Outcomes have limped lamely behind the SNP’s soaring rhetoric. The weaker the record, the greater the renewed promise.

But a party may still be returned to power with a poor record if there is no credible alternative. And the SNP has been blessed with very weak opposition. The Tories became Scotland’s second party in 2016 by presenting themselves as the true party of the union, casting Labour and Liberal Democrats as weak and untrustworthy on independence, making them the alternative party of government. Over the last five years, they have focused almost exclusively on opposition to an independence referendum, helping to narrow the political agenda and polarise debate.

So long as the union is centre stage, the SNP and Tories will benefit so long as Labour fails to articulate a clear alternative. Labour is damned for being insufficiently unionist by the Tories and too unionist by the SNP. The SNP never fails to point out that Labour worked with the Tories in Better Together during the 2014 Scottish independence referendum, in much the same way as an earlier generation of Labour politicians constantly reminded voters that the SNP brought down the Labour government in 1979 and let Margaret Thatcher into Downing Street. Labour has been unable to situate itself in the debate with a distinct position on the constitution.

Related: Scottish election 2021: a visual guide on what to expect

The pandemic has created an opportunity that Anas Sarwar, its new leader, has exploited skilfully by stressing the importance of “recovery”. Sarwar’s significantly improved poll ratings suggest he has been the star of the election, but rising leadership ratings have not been matched with rising levels of support for Labour. If Labour did push the Tories into third place, this would have significant implications for a prospective referendum. The SNP would much rather go into a referendum in which the Tories were the main opposition; a Labour revival would create problems for the SNP, especially if Labour were to offer an alternative to the current binary divide. This would open up debate with an option Labour could comfortably get behind, command broad public support by drawing votes from both independence and the status quo, and avoid the binary pit that would force the party into bed with the Tories again.

Devolution’s promise of “new politics” based on pluralism, compromise and consensus was always unlikely. The electoral system may have produced more Holyrood parties than Scotland returns to the Commons, but Holyrood is now more adversarial and polarised than ever. The narrow prism through which this election is viewed makes it very difficult to see that changing after this election.