In 1880, in the wake of the Midlothian campaign, the Liberals won 70.1 per cent of the vote and 52 of Scotland’s 58 parliamentary seats. In those days, it was no more than the party expected.

In 1865, though the franchise was a joke, the Liberals had won 85.4 per cent of votes cast; in 1868, 82.5 per cent. From the mid-19th century until the eve of the Great War, Scotland belonged to WE Gladstone and his heirs.

In 1955, as Tories always remind you, an alliance of Unionists, Conservatives, and National Liberals achieved 50.1 per cent of the Scottish vote. No one had managed such a thing since the advent of universal suffrage. For most of the 1950s, Conservatism was Scotland’s dominant creed.

That changed in 1964, when Labour won 43 of 71 seats. For 46 years, through 13 General Elections, the party never returned fewer than 40 members to Westminster. In 1997 and in 2001, it emerged with 56 MPs. For decades, Scotland was Labour. In the Commons, as often as not, Labour was Scottish. So where, as François Villon’s ballad doesn’t quite put it, are the natural parties of government of yesteryear?

By the 1950s, the Liberals were a one-man Scottish band in the person of Jo Grimond. By 1997, the Tories had not a single MP to show for almost half a million votes. In May this year, as you probably heard, the roof came in on Labour in Scotland. What had seemed immutable was laid waste.

In terms of share of the vote, it was Labour’s worst showing since 1918. The General Election was also the worst performance from the adherents of Liberalism since 1970. Tories, in whatever configuration, had not done as badly as they did in May, with 14.9 per cent of the vote, since the crushing defeat of 1865.

Anyone enduring a fit of the vapours over the SNP and its “one-party state” should bear these facts in mind. This is not a one-party state: this a one-successful-party state (or country). Besides, incipient totalitarianism wasn’t often mentioned back when Labour had its 56 MPs, the Scottish Office, all the biggest councils, and a flourishing quangocracy. That’s yesteryear for you.

Scottish opinion changes slowly, but a change, when it comes, is decisive. After each upheaval one party dominates the political landscape for years, sometimes for generations. The process is only roughly aligned, if at all, with the electoral ups and downs that decide the composition of the United Kingdom government. The history of politics in Scotland is akin to geological eras: Liberal, Conservative, Labour, rising and falling.

If all that’s so – and the record is clear enough – anyone waiting for “the rules of politics” to impinge on the SNP and burst Nicola Sturgeon’s bubble could be kicking their heels for a while. The idea that disenchantment over land reform, taxation, fracking, T in the Park, policing, the NHS or whatever will cause scales to fall from the electorate’s eyes is madly optimistic. Received wisdom is a thin sort of comfort blanket.

Let’s presume, nevertheless, that you’ve had it up to here with the SNP. Let’s say the indictments (freely available at all good outlets) have begun to hit home. Let’s assume you’ve lost faith in the party to which you gave your vote in May. You might understand the difference between legality and morality where a Michelle Thomson is concerned, but you’re still not happy. Perhaps a fracking moratorium isn’t good enough, or John Swinney’s promises on welfare cuts sound feeble. What now?

Labour got through most of its 46 years of dominance sustained by a single thought: our vote has nowhere else to go. The party was not loved universally. Its manner of doing business was not greatly respected. Its failures were all too familiar. Labour was profoundly vulnerable, as we now know, to serious competition. But while it had the upper hand, one fact answered every critic. Those inclined to Labour had no alternatives.

When a real alternative presented itself, of course, all the old explanations for the party’s dominance turned out to be chimeras. The myth of “tribal loyalty” was the first to go. What became of that when Labour needed it in May? The claim to a unique understanding of Scottish needs was next. At the election, Labour was dismissed as a branch office. And at last its vote had somewhere else to go.

The SNP stands now where Labour once stood. It has crafted its rhetoric around the claim of indispensability: Scotland’s party, the real opposition, the only answer to austerity, and so on. This isn’t cynicism, necessarily: the language meets a demand. But the SNP’s dominance, its imperviousness to criticism in defiance of those revered “rules of politics”, has deeper roots.

In part, it has to do with the psychology of choices. Rejected alternatives do not become more appealing because a hope goes unfulfilled. The failure to win the referendum did not, as predicted, alienate the majority of Yes voters. It did not persuade them to “come home” to rejected Labour. Instead it bound them tighter than before to the one party that would keep the hope alive.

Ms Sturgeon has another advantage. It derives, ironically enough, from those who dislike her party the most. Or rather, it comes from their refusal to grasp that clinging to received political wisdom is ill-advised.

Where the SNP is concerned, the mistake seems to be addictive. A Holyrood majority? Couldn’t be done. Fifty six MPs? An impossibility. Ms Sturgeon immune to criticism? Just wait; the bubble will burst; any time now. What has always happened must always happen.

No one now talks as though a second SNP majority at Holyrood is an impossibility. Once broken, the rule cannot be restored. But if that’s the case, what is established political knowledge actually worth? If it’s simply a blind faith in precedent, the fate of generals forever fighting the last war awaits the enemies of Ms Sturgeon.

What’s evident, nevertheless, is that critics baffled by loyalty to her and her party have paid too little attention to Scotland’s political history. It says that when a party becomes as successful and as dominant as the SNP has become, the honeymoon, so called, does not end quickly. In that context hysteria over cults, madness, dupes, propaganda and one-party states is amusing enough, but irrelevant.

There will be plenty of setbacks ahead for the SNP. There will be failures and there will be controversies. The appointment with a second independence referendum cannot be postponed indefinitely: the fact will not have eluded Ms Sturgeon. It is passing strange, nevertheless, that those most opposed to self-determination are this week the people most determined to have a date put on the rendezvous. It resembles displacement activity.

The Nationalists have become a repository for hope and trust because, in the judgment of the majority, no other party deserves the job. There is nothing in the rulebook to cover that situation, perhaps because the rulebook was never worth very much to begin with.

Ms Sturgeon and the SNP are beyond serious challenge because they tore up those rules. That, it seems, is how political eras begin.