Brendan Nelson failed terribly as the Leader of the Opposition, and even moreso as the Leader of the Liberal Party. He was unpopular with both the public at large and within his own party, and as the errors and gaffes piled up, it became clear that his days were numbered.
The two front runners to replace him were Malcolm Turnbull and Peter Costello. Costello had previously been the Deputy Leader of the party under John Howard, as well as Treasurer, and was the favourite to win in most opinion polls and editorial pages. However, he declined to contest (and retired entirely from Parliament the following year), leaving Malcolm Turnbull to win the leadership in a canter.
Julie Bishop’s tenure as Deputy Leader continued under the new leader.