Perhaps the greatest source of frustration for opponents of the Scottish National party is the way it has remained popular even after eight years in government.
In recent weeks Labour, Conservative and Liberal Democrat politicians have lined up to highlight the Scottish government's failings, such as missed emergency health waiting time targets and falling literacy scores. Regardless, the SNP's opinion poll ratings have climbed above 50 per cent, even higher than during the 2011 landslide that gave it a majority in the devolved parliament.
"Governments tend to be come more unpopular as they mature but that hasn't applied to the SNP government at all," says Mark Diffley, Scotland director of Ipsos Mori, the polling company.
Analysts say a big factor in this defiance of normal political gravity is the way in which powers devolved to Scotland allow the SNP to be both ruling party and outsider. It can claim the credit for Scottish government achievements but blame shortcomings on its limited powers and on spending cuts imposed by Westminster, which funds most of the Scottish budget through a block grant - which also allows higher per capita spending than the UK average.
"They don't raise taxes and they don't decide to go to war," says Mr Diffley. "The things that tend to make governments unpopular, they don't do."
There is little doubt the SNP was boosted by last year's independence referendum, when it cast itself as a party offering a radically different and more equal future - and by the election of the down-to-earth Nicola Sturgeon as leader. Ms Sturgeon has broader appeal than her predecessor, Alex Salmond, whose deputy she was throughout the SNP's time in office.
"She is much less divisive," says David Torrance, a political commentator, noting that an Ipso Mori poll this week found 71 per cent of voters were satisfied with Ms Sturgeon's performance. "Salmond's ratings were high but never that high. Even many non-independence supporters like her and think she's doing a good job."
<
The tabular content relating to this article is not available to view. Apologies in advance for the inconvenience caused.
>But the independence referendum is by no means the sole reason the SNP finds itself in such a commanding position ahead of the general election. A vital ingredient in its success has been establishing itself as an effective ruling party after it first won power as a minority administration in 2007, says Henry McLeish, a former Labour first minister of Scotland. "They proved competent in government," he says.Mr McLeish adds the nationalists have also benefited from the weakness of their rivals, particular since 2011. Many Labour members say their party found it difficult to adapt after losing power in Scotland, struggling to come up with a coherent platform and to establish a clear relationship between its Scottish and UK leaderships.
"The SNP has done well but the lack of an effective opposition has made them look better than they are," says Mr McLeish.
With relatively low expectations in its early years in office, the SNP managed to maintain tight discipline and internal cohesion. "There have been no major cock-ups; nothing you could say spells a government out of control," says Mr Torrance, who has written unauthorised biographies of both Mr Salmond and Ms Sturgeon.
The nationalists have also produced government that "broadly fits what most Scots want", adds Mr Torrance. Headline policies such as a freeze on local government tax, free tuition for university undergraduates and free prescriptions are widely popular.
Most voters have also seemed willing to forgive the promises they broke, such as Ms Sturgeon's 2006 pledge to cancel student debt and reintroduce grants.
However, Mr McLeish and other Labour critics strongly contest the SNP's claim to be Scotland's party of social justice. "There is nothing progressive about the SNP," says Jim Murphy, Scottish Labour leader. "They have not done anything during the eight years they have been in power to redistribute to the poor or those who struggle."
In answer, SNP members point at the Scottish government's work to cancel out unpopular UK welfare policies such as the so-called bedroom tax, under which housing benefit was cut for council tenants judged to have too much space. The party also used its newly gained control over stamp duty on property to replace it with a tax that put more of the burden on owners and buyers of expensive homes.
But while the SNP's popularity suggests it could next year win another majority in the Scottish parliament - a feat once thought almost impossible under the proportional representation system - Ms Sturgeon faces increasing challenges.
The promised transfer of greater tax-raising powers to Scotland will force the party to choose between its rhetoric on redistribution and the risk of upsetting middle-class voters. Ms Sturgeon has raised expectations among more leftwing supporters with promises of "radical land reform". Increasing strains on councils are likely to raise pressure to revisit the thorny challenge of local taxation. And ever-rising demand will place added burdens on an already stretched health system.
A Labour MP facing redundancy on May 7 complains the SNP is in a "Teflon phase". Some day, the political mud may begin to stick.
© The Financial Times Limited 2015. All rights reserved.
FT and Financial Times are trademarks of the Financial Times Ltd.
Not to be redistributed, copied or modified in any way.
Euro2day.gr is solely responsible for providing this translation and the Financial Times Limited does not accept any liability for the accuracy or quality of the translation