EVENTUALLY, you just have to apologise. When confronted about the ferries fiasco at Tuesday’s SNP leadership hustings, Humza Yousaf had no other credible option. “We’ve got to put our hands up,” he said.

What else could he say? The ferries mess has become a fist-gnawing embarrassment for the SNP; a public humiliation; a dry-dock Grand Designs debacle. It’s running three times over budget, the vessels will be delivered five years late and the key parties have traded acrimonious barbs. Even at his most sardonic, Kevin McCloud would struggle to convey the sheer folly of it all.

Because it keeps generating headlines like a lurid soap opera, the ferry saga will be a liability for whomever becomes the next First Minister.

But it’s not the only one. The Deposit Return Scheme is widely derided; NHS figures are a monthly drumbeat of failure; we’re nowhere near getting to grips with drugs deaths; homelessness is out of control; and progress on closing the attainment gap has been glacial.

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You can’t keep blaming the pandemic forever, particularly when there are unfavourable comparisons to be made with England, such as on two-year waits for operations.

The leadership campaign has also yanked back the curtain on divisions in the party itself.

This is a grizzled old government. It would probably do it a lot of good to spend a spell in opposition and some other parties are predicting exactly that, as if next year’s general election were a foregone conclusion.

But I’m not so sure. Nicola Sturgeon may be leaving, but what hasn’t changed is the galvanising power of independence.

Independence is the glue of the SNP, the cohesive influence that holds the party together and binds a large proportion of voters to it, even when the SNP’s actions in government are underwhelming.

We’ve heard a great deal in the last month about Nicola Sturgeon’s eight election wins at the head of the SNP. She’s won three general elections, two Scottish, two local and a European.

HeraldScotland: Nicola SturgeonNicola Sturgeon (Image: FREE)

There’s no question that the fortunes both of her party and the independence cause have been closely linked at times to her personal popularity. Her resignation has already diminished support for the SNP. Most polls since she resigned show that general election support has dropped below 40 per cent for the first time in years.

What we don’t yet know, though, is how many independence supporters will continue to back the SNP even if they don’t much like the new leader, just because the SNP is the best vehicle for achieving independence.

The worst-case scenario for the SNP is that the new First Minister, freighted with woes, presides over a further erosion of support, both for party and cause.

So how low could SNP support go before we hit a solid bedrock of unwavering support? This is the key question. The lowest vote share the SNP got at a national election under Nicola Sturgeon was 37 per cent in 2017.

She was not then at the height of her popularity and had made a tactical error by focusing early in the campaign on demands for another referendum. Using that as a sort of benchmark, then, you could speculate that even on a bad day, the SNP could command 30 to 35 per cent of the vote and possibly more, thanks to loyal independence supporters.

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If so, that may well be enough to out-poll any other single party. That’s quite a thought: that even in decline, the SNP could continue to come out on top.

This is essentially because of the structural advantage the SNP enjoys: with the Scottish electorate split roughly down the middle on independence, the SNP commands the lion’s share of votes on one side while the pro-UK parties divide the spoils three ways on the other side.

Admittedly, emerging as the largest party wouldn’t be much of a win for the SNP if their votes didn’t translate into a majority of seats, but it underlines their potency as a force in Scottish politics.

Naturally there are many variables. For instance, with independence looking an ever more distant prospect, even committed indy-backers may be more willing to lend their vote out in 2024, backing Labour to get shot of the Tories.

And depending on who gets elected as the next leader and what their priorities are, young independence-supporters may be alienated by a new SNP government that placed less emphasis on climate change or trans rights. We don’t know how those things could affect the SNP’s polling numbers or its ability to win elections.

Even so, I’m inclined to think that as the dominant force in Scottish politics, the SNP isn’t finished yet. The huge difficulty the anti-independence parties in Scotland have had for the last 15 years has been enthusing people about the status quo when the SNP is peddling visions of wind-powered Nordic egalitarianism on the other side of the rainbow.

I don’t see it being any easier for them in 2024. Labour pose the greatest threat to the SNP in 2024’s general election, but Scottish Labour needs a vision of its own to sell. Anas Sarwar is still to flesh out his offer to Scottish voters beyond “vote for me to kick out the Tories”.

The SNP are also consummate campaigners. The relentless nationalist mantra of “standing up for Scotland” will be in use long after Nicola Sturgeon has departed the stage. Not for them will there be any messy compromises to reach with a Westminster sister party.

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They’ll ruthlessly exploit Labour’s acquiescence on Brexit and the discomfort Mr Sarwar and his colleagues feel about Keir Starmer’s strategy of pandering to Red Wallers.

And we should of course never underestimate the UK Government’s talent for pushing Scottish voters into the arms of the SNP. They have form for insensitive and ill-judged behaviour towards Holyrood.

The gender recognition reform bill and the Deposit Return Scheme may not be wildly popular measures in their own right, but if the UK Government gets a taste for knocking back Holyrood laws and blocking the implementation of Holyrood policies, voters will start to resent it, especially when it’s repackaged by the SNP as an assault on Scottish democracy.

So things are bad for the SNP, worse than they have been in years, but finished? No, not quite.