His colleagues were growing impatient and his opportunity seemed behind him. Peter Costello is wise to farewell politics.
PETER Costello's quip that both sides of Parliament were happy that he's on the way out has, as he must know, a lot of truth in it.
Malcolm Turnbull must have had trouble containing his delight. For him, Costello's presence has hung like a black cloud, provocative, even menacing, a constant reminder that bad polls would make the former treasurer more attractive as an alternative.
The Government has had its own concerns about Costello. With the economy the big issue in the run-up to the election, his economic credentials potentially had the possibility - it was never any more than that - of reviving the Liberals' fortunes.
For Costello, hearing the tributes must be bitter-sweet. He achieved so much, but fell short of the ultimate prize. Partly that was because of John Howard's refusal to accept that his government needed new leadership. But Costello can only transfer so much of the blame to Howard: he also failed to convince his colleagues that he should take over.
Yesterday the Howard-Costello tension was still on display. Howard's tribute was almost grudging, emphasising the achievements of the Coalition government rather than of Costello himself.
In opposition, Costello has appeared conflicted. He passed up the leadership twice. His intervention in the political discourse was sometimes intense, but much of the time he was silent and withdrawn.
Immediately after the election he indicated he would seek a new life, and then failed to find one. Eventually he decided he could not stay in this half-world forever.
His decision is sensible. His colleagues were becoming impatient with him; the political teasing had lost its excitement. Last year, many Liberals wanted him to be leader; recently, despite Turnbull's problems, they had become much more critical of him.
Even if he had become leader before next year's election - and that would have involved bringing down Turnbull, not an easy feat - he probably would not have defeated Kevin Rudd, and where would that have left his reputation? Anyway, after all those years in government, the job of opposition leader, with its constant demands, would probably have been an ill fit for a man who sometimes looked to have lost interest in politics.
As for waiting until Turnbull lost the election and taking over then, Costello probably sensed the caravan might have moved on, with Joe Hockey or someone else appearing a better bet.
Costello has wound up the hardliners in the Liberal Party, which has added to Turnbull's grief. He will still be in a position to do so, but Turnbull can reasonably expect that the Costello influence will be muted now everyone knows he won't be around beyond the election.
But Turnbull should go easy on the champagne. Costello only crystallised views that are strong in the party, for example on emissions trading. They will continue to be testing for Turnbull to manage or resist.
As aspiring leader, Costello had trouble defining what he stood for, outside his economic area. It was one reason for his failure to go further. Turnbull is suffering from the same problem. He is having great difficulty marking out what his Liberal Party stands for. He now has at least more air in which to do it, but it remains a formidable challenge.