Mr Turnbull has come under fresh fire from Brendan Nelson, the man he deposed. In an article in today's Herald Dr Nelson implicitly criticises Mr Turnbull for yielding to the Government on emissions trading.

Without naming Mr Turnbull, Dr Nelson writes about the Liberal Party's future directions.

''The adoption of a policy position that violates principle to avoid political pain demeans the nation's best interests and diminishes us,'' he writes.

''Australians will always know and reject those who seek power for its own sake.''

Senior Liberals rallied around Mr Turnbull yesterday, saying that moves against him within the party would endanger marginal seats in the next election.

But his authority within the party could well come under scrutiny in a meeting of the shadow cabinet today.

A Newspoll published today shows his approval rating has fallen to 26 per cent from 33 per cent.

The Coalition is set to vote against the Government's emissions trading scheme on Thursday. But the Liberal Party remains split over whether it should vote against the scheme if the Government returns it to the Senate for a second time in November.

Amid the multiple challenges confronting him, Mr Turnbull will have to juggle three thorny health measures that are expected to go to a crucial vote in the Senate.

These are the Government's budgetary measures to extract big revenue and savings from the alcopops tax, the withdrawal of health insurance rebates for those on high incomes, and changes to the Medicare safety net that will expose many patients having IVF and eye procedures to big increases in out-of-pocket costs.

Mr Turnbull's decision not to oppose the alcopops tax stoked a rebellion among some Coalition MPs, including the Liberals' Wilson Tuckey and National MPs.

The Coalition had accused the Government of cloaking the 70 per cent tax grab with questionable claims of reducing teen drinking.