In the next seven months, first-term Coalition governments will face the voters in Australia’s two most populous states. Both governments have had leaders fall by the wayside since they came to power nearly four years go, and both face Labor oppositions that, barring any late accidents, will have broken with recent tradition in standing by their leaders over the full course of a term.

So much for the similarities. According to two polls released this week — one by Galaxy for New South Wales in The Daily Telegraph, the other by Newspoll for Victoria in The Australian — the governments stand worlds apart so far as their electoral prospects are concerned. Both polls had two-party preferred ratings well into landslide territory at 55-45, but the advantage lay with Mike Baird’s Coalition government in the former case, and Daniel Andrews’ Labor opposition in the latter.

The results are well in line with recent trends, as illustrated by the aggregations of Newspoll, Galaxy, ReachTEL, Nielsen, and Essential Research polling in the charts below. This tells a particularly straightforward story in the case of New South Wales, where Coalition support has steadily descended from unprecedented early-term heights with two interruptions: in early 2013, when the Independent Commission Against Corruption was applying its blowtorch to the activities of Eddie Obeid, and in the wake of Mike Baird’s ascent to the leadership four months ago.

The latter movement has been a fairly routine example of what might be called the give-the-new-bloke-a-fair-go effect, another of which can be seen from April to July 2013 in the Victorian chart. If the Coalition bounce that followed Denis Napthine’s rise to the leadership is any guide, we can expect the slow trend to Labor to resume in New South Wales at any tick of the clock.

Even allowing for that qualification, it’s a startling fact that a generally well-behaved first-term Liberal government in Victoria appears headed for the guillotine, while its scandal-ridden counterpart in New South Wales need only fear having its wings clipped. The disparity in perceptions of the two parties is also evident at federal level, with the BludgerTrack poll aggregate showing no change in Labor’s relative advantage of 5% in Victoria from last year’s federal election.

Whereas Queensland’s conservative inclination reflects its unusually large non-metropolitan population, and Western Australia’s bespeaks the wealth it has accumulated through the mining boom, there is no readily obvious socio-economic reason why the voters of New South Wales should be turning to the Coalition in such greater numbers than Victoria’s. On the main demographic pointers to aggregate voting behaviour, such as income and ethnic diversity, the results for the two states in the 2011 census are barely distinguishable.

One thing that can be said with certainty is that the gap, or at least the present scale of it, is a recent phenomenon. A few generations ago, it was the Liberal Party that felt cause to regard Victoria as its “jewel in the crown”, as long-serving premier Sir Henry Bolte famously described it. From the Labor split of 1955 to the second Fraser landslide of 1977, the federal two-party vote for the Coalition was between 3% and 10% higher in Victoria than New South Wales. At state level, Labor had to wait until the 1952 election before it was first able to govern with a parliamentary majority, and its defeat three years later marked the beginning of 27 years in opposition.

The great reversal since has unfolded in three phases. In the 1980s, Labor was finally able to achieve dominance in Victoria at state level, and its federal vote began to exceed that of New South Wales as often as not. Victoria’s long-term move to the Left appeared to solidify in the late 1990s, as the state’s voters stayed off the One Nation bandwagon in 1998, voted out Jeff Kennett’s government against all expectations in 1999, and delivered a two-party majority to John Howard at only one out of five elections between 1996 and 2007. The third phase, if that’s what it is, began with the federal election of August 2010, when Victoria swung 1.0% in favour of Labor under the leadership of Julia Gillard, while New South Wales went 4.8% the other way.

The only disturbance in the trend over the three decades was after the State Bank collapse, when Victorian Labor suffered a near-fatal reverse federally in 1990, and a landslide defeat at the state election of 1992 — to be followed in each case by a surprisingly quick recovery. No doubt the lesson to be learned from Labor’s experiences in Victoria two decades ago and New South Wales today is that the party remains electorally formidable for as long as it keeps its nose clean, but can expect particularly harsh treatment whenever it is perceived to be tainted by incompetence or corruption.

The primacy of demographic factors over the long term suggests that Labor’s strength in New South Wales will ultimately reassert itself. However, it won’t happen until the party has satisfied voters that it has substantially changed its ways, or at the very least done penance. For all the damage that the Baird government might be copping at ICAC, that time has clearly not yet arrived.