In the subsequent leadership struggle, Gorton was championed by Army Minister Malcolm Fraser, Government Whip in the Senate Malcolm Scott and Liberal Party Whip Dudley Erwin, and with their support he was able to defeat rivals Paul Hasluck, Les Bury and Billy Snedden to become Liberal leader even though he was a member of the Senate. He was elected party leader on 9 January 1968, and appointed Prime Minister on 10 January, replacing McEwen. He was the only Senator in Australia's history to be Prime Minister and the only Prime Minister to have ever served in the Senate. He remained a Senator until, in accordance with the Westminster tradition that the Prime Minister is a member of the lower house of parliament, he resigned on 1 February 1968 to contest the by-election for Holt's old House of Representatives seat of Higgins in south Melbourne. The by-election in this comfortably safe Liberal seat was held on 24 February; there were three other candidates, but Gorton achieved a massive 68% of the formal vote. He visited all the polling places during the day, but was unable to vote for himself as he was still enrolled in Mallee, in rural western Victoria. Between 2 and 23 February (both dates inclusive) he was a member of neither house of parliament.