In OTL, the 1961 federal election was very close: the Liberal Party won against Labor with 62 seats to 60, scraping victories in a few seats due to DLP preference deals.
The POD: the election goes slightly differently in a couple of seats, and Labor ends up in government with 62 seats to 60 instead. Robert Menzies is voted out after 12 consecutive years as Prime Minister and Arthur Calwell becomes PM. How goes the country from there?
(This WI was inspired by my musings that Kevin Rudd seems to me to be basically a modern-day Calwell to Howard's Menzies... except that Rudd won.)