2008 Mayo by-election

Downer first won the seat of Mayo at its creation at the 1984 federal election. He retained the seat at each subsequent election. The 2007 Liberal two-party-preferred vote of 57.1 percent was at the time the narrowest in the seat's history. Except for 1998, the seat was won at each election by the Liberals on primary votes alone. Despite this, the Australian Democrats and independents have traditionally polled well, including two elections where the Democrats and independent Brian Deegan came second.[4] At the 1998 election the Democrats reduced the Mayo Liberal margin to just 1.7 percent.

At the 2007 federal election, Downer retained his seat against his main Labor Party competitor by a two-party preferred vote of 57.06 percent to 42.94 percent.[5] However, the opposition Labor Party defeated the incumbent Liberal-National coalition government, the first change of government in over 11 years. Downer had served as Foreign Minister throughout the duration of the previous government. He was also Liberal leader and leader of the opposition for several months in 1994.

On 3 July 2008, Downer announced his intention to resign his seat. He officially resigned from parliament on 14 July.[6] He, with Mark Vaile in Lyne, became the next former Howard government ministers returned at the 2007 election to resign their seats. Peter McGauran had done likewise earlier in 2008.

Eleven candidates contested the by-election. They are listed below in ballot order.[7]

• Australian Greens – Lynton Vonow, Adelaide Hills resident, school services officer.[8]
• Conservatives for Climate and Environment – Rachael Barons.
• Independent – Bill Spragg, Adelaide Hills councillor and lecturer in information technology at TAFE SA, who had also contested Mayo in 2001.[9][10][11]
• One Nation – Mathew Keizer, Adelaide Hills resident and domestic community support worker.[12]
• Independent – Mary Brewerton, retired nurse, contested Mayo for Labor in 2007.[13]
• Australian Democrats – Andrew Castrique, Adelaide Hills resident, school laboratory technician.[14]
• Liberal Party of Australia – Jamie Briggs, former Howard government advisor[15]
• Independent – Malcolm Ronald King, retired.
• Family First Party – Bob Day, businessman and former Liberal Party member.[16]
• Democratic Labor Party – David McCabe, clerk.
• Independent – Di Bell, anthropologist and author.[17][18] South Australian independent Senator Nick Xenophon gave support to Bell's campaign.[19][20]

Labor opted not to stand a candidate.[21]

The candidature of Liberal Jamie Briggs was criticised because of his role in controversial industrial-relations policies and reports that some Liberal Party colleagues were unhappy with his preselection.[22] Bob Day, who had held membership of the Liberal Party for 20 years and was the endorsed Liberal candidate for Makin in 2007, quit the party after failing to win Mayo preselection with 10 out of 271 votes,[23] claiming a "manipulated" preselection process.[24] Iain Evans, who came second to Briggs, agreed to some extent.[25]

The Liberals retained the seat despite a reduced 41.3 percent primary vote after suffering a 9.8 percent primary swing. Some commentators drew comparisons between this and the 2002 Cunningham by-election.[26] The Liberal two-candidate vote of 53 percent against Greens candidate Lynton Vonow compared to the previous election vote of 57.1 percent against Labor,[27] which turned Mayo from a fairly safe seat in to a marginal two-candidate seat.[28] The reduction of 4 percent cannot be considered a "two-party/candidate preferred swing" − when a major party is absent, preference flows to both major parties does not take place, resulting in asymmetric preference flows.[29][30]

Eight years later, Rebekha Sharkie of the Nick Xenophon Team was successful in defeating Liberal incumbent Jamie Briggs in Mayo at the 2016 federal election with a 55 percent two-candidate vote to the Liberals' 45 percent two-candidate vote, a reduction of 17.2 percent. Additionally, Mayo became a marginal two-party seat for the first time with the Liberal two-party vote reduced to 55.4 percent, a two-party swing of 7.2 percent.

• List of Australian federal by-elections

• "2008 Mayo By-election". ABC.