South Australian politics rarely takes a central position in national news, but this Saturday’s state election will be watched much more closely than usual for potential federal implications.

It is shaping up as a perfect storm for a struggling Liberal party: under pressure from a popular first-term Labor government, while One Nation eats into the Liberal base. The election will be a first test of One Nation’s growing support nationally, with federal polls showing Pauline Hanson’s party regularly outpolling a weakened Coalition.

One key unknown is how preferences will flow in seats where One Nation is in the final preference count, given the Liberal party’s decision to put it above Labor on how-to-vote cards.

All six South Australian polls published this year have shown Labor well out in front, with One Nation leading the Liberals.

But there has been rather a lot of variation. The Labor primary vote has ranged from 35% to 44%. One Nation was more than 10 percentage points ahead of the Liberals in the Roy Morgan poll, but just one point in two earlier polls. It seems One Nation has mostly picked up support from the Liberals, but Labor’s vote has also dropped since the peaks of 2025.

The most recent survey, an Advertiser/YouGov poll published on Wednesday, gave Labor 38% of the primary vote, with One Nation on 22% and the Liberals on 19%.

We have no precedent for this sort of polling trend, so it is hard to know how the results will play out.

If One Nation polls above 20% across the state, it is likely to reach 30-40% in a number of regional seats, and thus will likely make the top two. If it is in that contest against a Liberal candidate, preferences from Labor and other parties on the left would be critical, and those are unlikely to flow strongly one way or the other.

The Liberal leader, Ashton Hurn, has justified the decision to put One Nation above Labor by saying her party is “in the business of getting rid of the ALP”.

“This is a vote of no confidence in the government. And that’s who I’m focused on defeating at the election on Saturday.”

But if Liberal support drops as far as the polls have suggested, the remaining Liberal voters may well elect a One Nation candidate over their Labor rival in some seats.

The South Australian Liberal party has won only one election in the last quarter-century, taking power in 2018. Labor won power under Peter Malinauskas in 2022, and his government has proved generally popular, even allowing for the recent patchy polling.

Late last year this election was looking a bit like some recent Western Australian elections: Labor winning a large majority against a weakened opposition, which is reduced to a mere handful of seats. But things have become more complicated as One Nation has gained ground.

We don’t know if One Nation will poll as well as opinion polls have suggested. Some voters may return to their traditional home, and the presence of known local members may slow the flight of Liberal voters to One Nation in some places. But if One Nation gets over 20% of the vote, that will have a momentous impact, particularly in regional areas and the outer suburbs where it generally performs best.

Thirty-four of South Australia’s 47 seats are in Greater Adelaide, and the Liberals now hold just six of those seats, all quite marginal. The party looks to be in a lot of trouble in seats such as Unley, Morialta, Colton and Morphett.

The Liberals’ regional seats have traditionally been their safest, but in current circumstances some of those are in danger from independents as well as One Nation.

A number of regional seats are already held by independents and there are serious challengers in seats such as Flinders and Finniss. One Nation may stand a chance of winning seats such as Chaffey, a rural seat stretching to the Victorian border.

Labor is not likely to lose any seats to One Nation, but in some outer suburban electorates such as Taylor and Elizabeth we could expect to see a Labor v One Nation contest.