successful at the 2016 federal election, despite having unsuccessfully mounted a High Court challenge against newly implemented Senate voting reforms which included the removal of group voting tickets, a feature which was crucial to the election of Day at the previous election. Though the South Australian Senate Family First vote was reduced to just 2.9% (down 0.9%), as the election was a double dissolution, the quota to be elected was halved. Day got to the 7.7% quota largely from Liberal preferences when the Liberal's 5th candidate Sean Edwards was eliminated from the count, largely due to the fact the Liberal how-to-vote card recommended Liberal voters to preference Family First. Electing only six Senators per state at a non-double dissolution election, the 12th and last spot in South Australia at this election came down to a race between Day and Labor's 4th candidate Anne McEwen. McEwen solidly led Day for the overwhelming majority of the count, until count 445 of a total 457. However, upon Edwards and then One Nation candidate Steven Burgess being eliminated at count 445 and 455 respectively, leaving only McEwen and Day remaining, Day had collected enough preferences to overtake and narrowly defeat McEwen − by just a couple of thousand preference votes. The nationwide Family First Senate vote was 1.4% (up 0.3%). Elected to the 12th and final South Australian Senate spot, he was entitled to a three-year term. Due to the failure of his home construction business, Day resigned from the Senate on 1 November 2016 and a replacement was expected to be selected in the following two to three weeks. In April 2017, the High Court found that he had been invalidly elected to the Senate at the 2016 election because the leasing arrangements for his electoral office had breached section 44 of the Constitution making him ineligible for the Senate, leading to a special recount of South Australian senate ballots to find a replacement. On 13 April 2017 Lucy Gichuhi was declared the new South Australian senator in place of Day, following a recount of ballots. Her appointment was challenged by the Australian Labor Party but the High Court rejected the challenge as to whether she has renounced her Kenyan citizenship or retained a dual Kenyan and Australian citizenship. Federal by-elections since 2004 Following the resignation of Mark Latham and their acquisition of a Senate seat in 2004, Family First contested the 2005