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Labor won a landslide victory in Victoria, Julia Banks abandoned the Liberal Party, the federal budget will be delivered early and Parliament will sit for only 10 days in the first eight months of 2019 — just another messy week in Australian politics.

What does it all add up to?

Over lunch a few weeks ago, Sam Roggeveen, director of the Lowy Institute’s international security program, told me that Australia’s main political parties were in trouble. This week, I went back to Sam for some additional insight.

So what do you make of the week’s head-spinning political developments?

They say history happens slowly and then all at once. I think the convulsions we are seeing in Australian politics right now — in fact , since John Howard was defeated in 2007 — are a culmination of decades-long trends that center on the slow decline of our two big political parties.