AnalysisSteven Marshall's departure leaves political parties fighting for the seat of Dunstan
Liberal-held inner suburban seats have become increasingly rare across Australia's capital cities.
Between the rise of teal independents and the Greens, plus traditional contests with Labor, one by one MPs from the right have lost electorates at both state and federal elections.
And the looming contest for the South Australian seat of Dunstan in Adelaide's inner east shapes as being another challenge for the incumbent Liberal Party.
Former premier Steven Marshall's decision this week to leave parliament sometime soon, but with a date yet set, arguably presents Opposition Leader David Speirs with the biggest test of his tenure to date.
Namely, trying to hold South Australia's most marginal seat at a mid-term by-election.
While it is unlikely a teal candidate will be in the fight, the majors will be fighting the Greens, a party that could prove pivotal in deciding the result.
Greens vote could be crucial in Dunstan
Greens candidate Kay Moncrieff secured more than 13 per cent of the vote at the 2022 state election, which was a swing of over 4.5 per cent on the 2018 result.
And while it's fraught to compare federal and state outcomes, two months later in the overlapping federal electorate of Sturt, the Greens won more than 16 per cent of the vote as Anthony Albanese swept to office.
Why does this matter?
Because historically preferences from the Greens flow more towards Labor than the Liberals, which bolsters the Australian Labor Party's (ALP) chances of snatching Dunstan if the trend continues.
That means for the Liberals to hang onto the seat, the party's primary vote likely needs to be in the mid to high 40 per cent range.
And that's without the benefit of an incumbent candidate.
Mr Marshall recorded 46.7 per cent of the vote at the 2022 election and only hung onto the seat by 260 votes from Labor's Cressida O'Hanlon once preferences were distributed.
Questions could be raised about the future of Mr Speirs's leadership if the party loses the seat it has held since 2010.
Not only is it a test for Mr Speirs, but it is also one for Premier Peter Malinauskas and Labor.
Health set to be a key campaign issue
The by-election could show how much of the gloss has come off the ALP after winning two elections in a matter of weeks in 2022.
The Liberals are attacking the state government's ability to deliver on its core 2022 state election promise to "fix the ramping crisis", with the number of hours lost to ambulance ramping outside emergency departments ballooning to record levels in recent months.
To counter that, Labor is messaging that it is the only party with a plan on health.
With that in mind, it was no great surprise the formal confirmation Ms O'Hanlon would again be the ALP candidate in Dunstan came at the new ambulance station under construction on the corner of Portrush and Magill Roads in the heart of the electorate on Thursday.
Labor will also hope for a halo to hang over The Parade thanks to AFL Gather Round. Norwood Oval hosted two matches last April and will do so again this year, in conjunction with the rebirth of the food and wine festival.
Given the narrow margin of 0.5 per cent Dunstan now rests on, we're already seeing the situation where the major parties are seeking underdog status.
Picking up a seat at a by-election while in government is no small task, but SA Labor does have form — achieving that feat in December 2014.
Current Human Services Minister Nat Cook secured a nine-vote win in the Fisher by-election following the death of independent Bob Such. Preferences proved decisive in that contest.
Would the party be best placed to continue to drive people toward the ALP with the second stroke of their pencil on the ballot paper?
Or, now the Liberals have formally pre-selected moderate Anna Finizio, would the preference question become harder to answer for the Greens, who are set to formally announce former Sturt candidate Katie McCusker as their candidate for the Dunstan by-election?
Whatever happens, the minor party may have a major say in who the next member of Dunstan will be.