Nahan entered politics at the 2008 Western Australian state election when he defeated incumbent Labor MP Tony McRae for the seat of Riverton in southern Perth. Nahan served as the Trustee of the Parliamentary Superannuation Board and was Chairman of the Economics and Industry Standing Committee in State Parliament from November 2008 to August 2012. As part of the Economics and Industry Standing Committee, Mike Nahan presided over the Kimberley Ultramarathon Inquiry, an Inquiry set up to understand why five individuals received extensive burns. It was later determined that the fire was caused by an out of control prescribed burn being conducted by FESA, El Questro, the WA Police and the James Gino Salerno family, a cult residing around Kununurra. After the Liberal/National government was reelected at the 2013 Western Australian state election, Nahan was promoted to cabinet as Minister for Energy, Finance, and Citizenship and Multicultural Interests by Premier Colin Barnett.
Treasurer of Western Australia
Nahan was appointed as the Treasurer of Western Australia on 14 March 2014 following the resignation of Troy Buswell. His first budget as Treasurer was delivered in May 2014. As Treasurer of Western Australia, Nahan presided over the loss of the state's AAA credit rating in August 2014 when state debt was downgraded to AA1, and an unemployment rate of 6.5% in March 2017.
Leader of the Opposition
The Liberal government was roundly defeated at the 2017 state election, suffering the worst defeat of a sitting government in Western Australian history. Notably, the Liberals' support in Perth almost melted. The Liberals were cut down to only nine seats in the capital, including Nahan's. Following the defeat, Barnett resigned as WA Liberal leader and returned to the backbench. Two days after the election, outgoing minister Bill Marmion indicated that Nahan had the most support in the much-reduced Liberal party room to succeed Barnett. He was elected unopposed as Liberal leader, and hence Leader of the Opposition, on 21 March, with outgoing Deputy Premier Liza Harvey remaining deputy leader. Nahan has been compared to Ned Flanders, a character from The Simpsons, with The West Australian cartoonist Dean Alston drawing him in the style of the animated television show. Nahan announced on 12 June 2019 he was stepping down from the parliamentary leadership of the Liberal Party. When asked who he will be backing as his replacement, he said it would be up to the Liberal party room to make that decision. Nahan also said that he had always planned to step down before the 2021 election, meaning that he never intended to take the Liberals into the campaign. He however disputed the suggestion that he was "warming the chair". His deputy, Harvey, was elected unopposed as party leader on 13 June 2019. He is only the fifth WA Liberal leader not to take the party into an election. Soon after Harvey was elected his successor, Nahan became Shadow Minister for Planning in Harvey's shadow cabinet.
Taxation and citizenship issues
In 2018, Nahan revealed a substantial disputed liability, believed to be potentially hundreds of thousands of dollars, to the United States Internal Revenue Service. Despite being a member of the Western Australian Legislative Assembly since September 2008 and Treasurer in the Barnett Government for three years, this possible liability was only disclosed in 2018 during a debate over eligibility of dual citizens. During the debate, Mike stated that he no longer held a U.S. passport but was unable to renounce his American citizenship until the debt was resolved. The issue arose in 2010 when the IRS changed the way in which it calculated liability from Australian superannuation recipients. Nahan is reported to be one many thousands of U.S. citizens caught up in the changes and is awaiting the outcome of several court cases in the United States where lawyers are confident that, if successful, his liability will be expunged. For Liberal Party colleagues the issue raised further concerns about his ability to lead the decimated party in parliament to the next Western Australia election expected in 2021.
