AT FIRST glance it looked as if Malcolm Turnbull, Australia's opposition leader, had fired a deadly bolt at Kevin Rudd, the prime minister. In blocking the government's legislation on climate change, Mr Turnbull seemed to thwart the prime minister on the issue he has made his signature since leading the Labor Party to power in 2007. Mr Rudd has wanted the scheme, which is to set targets for Australia's carbon-emissions reductions, ready for December's climate conference in Copenhagen. But Mr Turnbull might have thrown a boomerang, making him victim of his own attack.

Mr Turnbull is a lustrous figure in Australian politics. Having entered parliament only in 2004, less than a year ago he took over the leadership of the conservative Liberal Party. He promised to shift the opposition's main party back towards the centre, after more than a decade tacking to the right under John Howard. An ex-journalist and lawyer, who made a fortune in Sydney's business world, Mr Turnbull once led Australia's republican movement. But politics has dulled his sparkle. A poll released on August 10th showed only 26% of voters approving of his performance, a plunge of 18 points since mid-June. Almost four times as many voters prefer Mr Rudd as prime minister. The figures reflect two setbacks, each partly of Mr Turnbull's own making.

In June, Mr Turnbull called for Mr Rudd's resignation, citing a leaked e-mail about a plan to help car-dealers stricken by the credit crunch. The e-mail purported to show that the prime minister's office had asked the Treasury to help a friend of Mr Rudd's. But on August 4th Godwin Grech, a Treasury official who testified about it to parliament, confessed that he had faked the document himself. Mr Grech, it emerged, had shown it on June 12th to Mr Turnbull, who then believed it to be real. Mr Grech has since been hospitalised for depression. A report by the federal auditor cleared Mr Rudd of any wrongdoing.

The “OzCar affair” has dimmed many Liberal parliamentarians' view of Mr Turnbull's judgment. A television profile aired on August 3rd hardly helped: by chance, the cameras were in his office the day the forgery was exposed. Peter Costello, a senior Liberal who once coveted Mr Turnbull's job, has groused about his lack of caution. Divisions have sharpened between the party's centrist wing and the Howard-era hardliners who resent Mr Turnbull's ego and his reformist instincts.

The same divisions have shaken Mr Turnbull's bid to shape the Liberals' approach to climate change. Like the government, he supports a cap-and-trade scheme, allowing polluters to buy and sell permits for their carbon emissions. Such legislation has already passed the parliament's lower house, in June. But conservatives contend the scheme will damage business and farming and send jobs offshore. Wilson Tuckey, one of them, accuses Mr Turnbull of “inexperience and arrogance”.

To placate them, Mr Turnbull committed his coalition to voting against the bill when it came before the upper house, on August 13th. This aligned the Liberals with the Greens, who think the legislation too weak, and denied it a majority. The government can reintroduce the bill later this year, then call a general election if it is defeated a second time. Given his coalition's disastrous polling, Mr Turnbull is desperate to avoid that. He says he will negotiate amendments with the government when the legislation returns in November. Even if Mr Rudd's scheme survives then, there is no guarantee that Mr Turnbull's leadership will be so lucky.