My impression is there was a Trump effect. The Australian Liberals allied themselves too closely to Trump - Trump then did the dirty on them by putting tariffs on Australia despite the US running a trade surplus with Australia.
Even if it's just 5% of people thinking "Why are you allied with people who want to hurt us?", that's enough to swing the election.
I believe the Australian Liberals were leading before Trump's inauguration..
For sure. The tariffs nailed the coffin shut.