After the Coalition was defeated at the 1972 election, Fraser unsuccessfully stood for the Liberal leadership, losing to Billy Snedden. When the party lost the 1974 election, he began to move against Snedden, eventually mounting a successful challenge in March 1975. As Leader of the Opposition, Fraser used the Coalition's control of the Senate to block supply to the Whitlam Government, precipitating a constitutional crisis. This culminated with Gough Whitlam being dismissed as prime minister by Governor-General Sir John Kerr, a unique occurrence in Australian history. The correctness of Fraser's actions in the crisis and the exact nature of his involvement in Kerr's decision have since been a topic of debate. Fraser remains the only Australian prime minister to ascend to the position upon the dismissal of his predecessor.