Whether you put your trust in the accuracy of opinion polling, or take the view that the only polls that count are the ones on election day, the past few weeks have unambiguously demonstrated that the Coalition’s recent era of national electoral ascendancy is now a thing of the past. The latest indication of the conservatives’ deteriorating stocks was Labor’s stunning upset win in a state byelection in South Australia on Saturday.

The southern Adelaide seat of Fisher, which was vacated in October by the death of veteran Liberal-turned-independent member Bob Such, had previously been won by Labor on only one occasion since its creation in 1970. Prior to the byelection, the seat would’ve been one Labor might have hoped, at best, to reel in at a particularly big election win at the high point of the electoral cycle. What Labor should not be doing is gaining the seat at a byelection held a few months short of its 13th anniversary in office. Yet barring a miraculous reversal in late counting, that is exactly what appears to have happened.

In gaining the seat, Labor under Premier Jay Weatherill has achieved what only the party’s most extravagant optimists would have thought possible as it braced itself for defeat at the state election in March — a majority of 24 seats in the state’s 47-member lower house.

The consensus view going into the byelection, which I articulated in Crikey on Friday, was that the Liberals indeed had a fight on their hands — but that the threat came from Daniel Woodyatt, an independent whose endeavour to promote himself as Such’s natural successor was boosted by the endorsement of Such’s wife. But Woodyatt fell somewhat short of expectations — compare his 22.5% share of the vote with the 38.5% for Such at the state election in March, 2014.

The most remarkable aspect of the result was the complete failure of the Liberals to gain any dividend at all from the nearly four in 10 votes that were there for the taking in Such’s absence. By contrast, Labor appears to have gained over 10% on the primary vote, and to have done only slightly less well on a two-party preferred vote that was at 42.7% in March in Labor-versus-Liberal terms.

The table below places the result in context by displaying the swings for or against the government of the day at federal and state byelections contested by both Labor and the Coalition since the election of the Howard government in March 1996. Results are respectively in blue and red for byelections at which the Coalition and Labor were in power, with a deeper shade indicating a federal rather than state byelection.

The chart shows swings to the government of the day to be less unusual than conventional wisdom might suggest, with the Fisher swing being the tenth such out of a total of 33. However, it’s rare for pro-government swings to be as big as that in Fisher, with the chart showing only two examples surpassing it.

What makes the Fisher result even more remarkable is that it should happen during the government’s fourth term in office.

Of the 10 pro-government swings, Fisher is only the second that did not occur in the government’s first term, the other being the far more modest swing at Western Australia’s Peel byelection in March 2007 (which, lest we get too carried away with Fisher’s implications, was followed less than 18 months later by the government’s defeat).

It is likely that the result partly reflects a feeling that Labor, having successfully negotiated its way back into office after an indecisive election result, should not be required to suffer the uncertainty of minority government.

Similar sentiments may have boosted the governments of Bob Carr and Steve Bracks in the byelections that share space with Fisher at the top of the table, Carr having come to power with a majority of one, and Bracks relying at first on the support of three independents.

However, that explanation only gets us so far. Credit is due to Labor, if not for its political successes as a government, then at least for choosing as its candidate Nat Cook — whose background as the director of a youth welfare foundation offered a refreshing change from the usual career mill of political staff work and union officialdom.

As for the Liberals, the state party is understandably keen to sheet home the blame to the Abbott government. There can be little doubt that this is largely justified — perhaps even entirely so. Nonetheless, a party room that faces another three excruciatingly frustrating years in opposition must be sorely tempted to find a scapegoat closer to home. In particular, it will be asking itself whether its leader Steven Marshall, who seemed to offer so much this time a year ago, has the requisite killer instinct to overcome the cockroach-like survival powers of the Weatherill government.