What happens to centre-right politics if One Nation continues to grow?

Allocating preferences to the 'untouchables', as the Liberals did, can accentuate that purity spiral, damaging Liberal as well as One Nation when it comes to preference flows.

It's also possible that the fact the Liberals and One Nation were fairly evenly sharing their minority 40 per cent of the vote signalled instability to some voters.

Given the overwhelming expectation that Labor would win, One Nation and the Liberals were really competing for the spoils of opposition. But voters do want oppositions that are fit for purpose.

Voters have certainly chosen to turn South Australia into something approaching a one-party state, suggesting they don't rate the opposition highly.

The combination of these defections, people's prior tribal allegiances, perceived instability, the 'anyone but Hanson' tendency, and the demographic locations where they occurred meant that, depending on who made the final two, preferences could disproportionately favour Labor.

And there were more metropolitan seats vulnerable to these forces, which is where Labor secured its outsized results.

That suggests that while the One Nation insurgency doesn't reduce the overall non-Labor vote, it interacts with the compulsory preferential system in a way that makes it even harder to win from the right.

We should not be surprised. In Europe, where proportional representation makes these dynamics easier to observe, there has been a concerted effort by both the left and centre-right to keep National Rally in France and the AfD in Germany out of government despite their large followings. Tactical voting in the UK and Canada has produced similar outcomes, neutering Reform and the Canadian Conservatives.

This election provides limited guidance for the non-Labor parties elsewhere. Victoria is next, but that will be an election where the government should fall. In that case the Liberals and One Nation may be competing for the spoils of government, not opposition.

If One Nation and the Liberals maintain their relative sizes then the question of who forms government and on what basis should dominate the campaign. Would there be a coalition, or a minority government, and whose name would go on the letterhead?

Like South Australia, Victoria is highly centralised. Will the same dynamics play out, with inner-metropolitan seats moving left and moves to the right elsewhere?

Preferences are likely to be raised as a wedge. In South Australia One Nation saw no advantage in a deal, but the Liberals allocated to them anyway, as though there was a deal. That likely affected preference distributions – though not in the intended way.