Incumbent party leader Harold Holt sensationally disappeared while swimming at Cheviot Beach near Portsea on the Mornington Peninsula of Victoria on 17 December 1967. William McMahon, the incumbent Deputy Leader of the Liberal Party was assumed to be his probable successor, however, John McEwen, the interim Prime Minister and leader of the Country Party (the junior Coalition partner), announced that he and his party would not serve in a government led by McMahon. McMahon subsequently withdrew.