Before Tony Blair's spectacular fall in the affections of the voting public, he won three general elections.

Two of them were landslides and for most of his first eight years in power his party defied the normal laws of electoral politics. There were no midterm blues, no by-election melancholy to deal with, and no serious run on the authority of his government (that came privately from his Chancellor in Number 11).

Blair's stranglehold on power and seeming invincibility rested partly on the chaos at the heart of a Conservative opposition which did not appear to know what it was for. There are echoes of this period in the current Scottish situation.

The SNP is preparing for Holyrood landslide number two. Despite the Nationalists being on the back foot on many policy areas, the public appear deaf to opposition attacks and seem immovable in their belief that nothing Labour says is worthy of serious consideration, never mind a vote. Yes, Kez Dugdale's task is as seemingly impossible as that which faced William Hague and then Michael Howard.

In some respects Labour's dilemma is worse than that of the Tories at a UK level, when Blairism seemed all-pervasive before succumbing to the opprobrium heaped on it after the Iraq war. The Tories revived for two reasons. The public became bored then apathetic and then hostile to Labour, who came to power on a platform anchored in trust and left to jeers that they had betrayed that trust. And the Tories did some serious thinking, the end result of which was a repositioning of the party to embrace a more modern Conservatism.

Staying with the analogy, does Scottish Labour merely have to wait for the public to become bored with the SNP and then align their policy agenda with that of the voters? Well, for one there is no sign that the current SNP administration will fall out of favour, no Iraq-like issue looms likely to lead to a fundamental re-assessment of credibility.

But by far the biggest obstacle to a future Labour victory is the fact the party is not seeking to replace the SNP's social democratic politics; rather it is attempting to offer another version of it.

I would suggest any future fall in SNP support might be to the benefit of the Liberal Democrats and Greens rather than Labour, who have now lost a base largely defined by support that was generational in nature. No more do the grandsons and granddaughters of Fife miners and Lanarkshire steelworkers follow the voting habits of their elders.

Kez Dugdale's politics are not a world away from those of Johann Lamont, Iain Gray and Wendy Alexander. They are essentially rooted in traditional Labour values and yet she, like them, struggles to persuade voters that Labour can actually be trusted with traditions it defined and championed.

That distrust can be found in the evidence of the ballot box, the now largely neutral political position of the STUC, and the way in which large numbers of third sector civic leaders privately gravitate towards the SNP. Labour has to overcome the feeling that there is something of the past about it and something of the future about the SNP.

The party's current income tax policy, like Johann Lamont's debate about how progressives should allocate finite resources, has been poorly framed to the extent that a legitimate point about whether progressive taxes are needed to improve public services looks like being lost in a wider debate about credibility.

The current SNP juggernaut is fuelled by a government widely viewed as competent and in tune with the times and by a mass membership boasting fresh faces of genuine talent. In the past, Labour conferences were packed with the most talented in the Scottish political firmament at a time when SNP gatherings had an awkward kailyard feel about them.

Labour has been at its most successful when it has carried itself with a pioneering air. Attlee was swept to power when voters felt he was the future and Churchill the past. Harold Wilson struck a chord with a Britain anxious to rid itself of stuffy aristocrats, ready to leave the Macmillans and Douglas-Homes behind. Tony Blair reaped the benefit of voters tired by 18 long years of Conservative rule. And yet all of these Labour leaders had programmes for government that struck a chord with voters. Scottish Labour hasn't struck a chord for a long time.

The party is threatened at this election with a confirmation of marginal status. If they are not to become permanently irrelevant they will have to build from basics. That involves recruiting new members, forging new ideas, connecting with those who have broken the generational link with the cause of Labour.

The task falls to Kezia Dugdale. It is unenviable and might yet prove impossible. That alone may well give her the longevity denied to her predecessors, who fell victim to a party which refused to accept they were no longer top dogs.

Analysis by Bernard Ponsonby, STV's political editor. He joined the station in 1990 and became political editor in 2000. He has presented most election, by-election, and results programmes over the last quarter-century.