It had to happen sooner or later, and last week it did. Prime Minister Kevin Rudd made a major blunder.

Telling an interviewer that the government had done everything it could to reduce prices, and petrol prices in particular, may have been politically realistic, but it was not the sort of thing prime ministers are meant to say.

For starters it was not literally true. As Brendan Nelson insists with increasing stridency, Rudd could knock 5 cents off the oil excise; for that matter he could abolish it altogether, and get rid of the GST while he’s at it. Of course to do so would be an act of criminal lunacy, but that’s never been an insurmountable barrier for a desperate politician, as Nelson continues to demonstrate.

Moreover, one of Rudd’s own officers, assistant treasurer Chris Bowen, has noted that in the forthcoming tax review the GST charged on the excise will be considered. This component has always been controversial. It has been argued that an excise is neither a good nor a service, so the GST should not apply to it; what the government is in fact doing is imposing a tax on a tax, a decidedly mean and tricky act.

However, since the petrol excise has been capped at 38 cents a litre since 2001, removing the GST would be worth just 3.8 cents, and the way prices are going by the time the tax review reports at the end of 2009 this will hardly amount to a hiccup in a hurricane.

Still, at least it would be doing something. The point here is that governments are simply not allowed to admit to impotence in the face of adversity. What Rudd should have said was that his government had acted promptly and tirelessly to implement all its promises aimed at giving motorists and consumers generally a fair go, at restraining prices and increasing competition on every front.

Of course there were some things, like the world price of oil, which no amount of effort from Canberra could affect, but this would not stop him and his ministers from spending every waking hour in searching for new ways to alleviate the burdens the punters — sorry, better make that working families — were suffering. In the meantime they should ignore the cheap tricks and the cruel hoaxes of the unscrupulous opposition and use their tax cuts and childcare benefits to their best advantage.

But by saying there was nothing more that he could do, Rudd implied that he was planning to do nothing, thus leaving a vacuum at the top.

Nelson, barely able to believe his luck, filled as much of it as he was able, but was regarded as inadequate even by The Australian’s dominatrix Janet Albrechtsen, who called upon his party to cast him aside like a worn out pair of crotchless leather knickers. And of course there was no real question of who should be the replacement; onto the scene, or rather into the National Press Club, burst Malcolm Turnbull, radiating availability. In metaphorical terms he flung himself at the feet of Albrechtsen and her fellow conservative groupies gasping “take me, I’m yours”. And there is little doubt that they would, if the choice was theirs alone.

The problem is that there is still a sizeable rump in the parliamentary party who constitute an ABM (Anyone But Malcolm) faction. They no longer have a majority in the party room but they have enough clout to make it clear that if Mr Moneybags tries to bribe and bully his way to the leadership the way he won his preselection in Wentworth, there will be blood on the floor.

It is now generally accepted that he will probably get it eventually, but first he will have to display patience, decorum and above all loyalty; qualities notably absent from his political career to date. Last week’s speech was aimed at showing the doubters that he had received the message.

His formula for recanting his previous condemnation of the petrol excise cut (he now accepted that it was “good politics”) was a clever one and his parading of his own commitment to the traditional Liberal basics of individual rights, choice and opportunity obviously went some way to reassuring the faithful that his leftish aberrations such as republicanism could be and would be controlled.

The performance moved Tony “People Skills” Abbott to declare that while he himself was now just another foot soldier, Turnbull had assumed Peter Costello’s ragged mantle as the party’s heir apparent, which could be taken either as an endorsement or as a warning: these days no-one wants to be compared to Costello the Yellow, the Prime Minister who never was.

But the circumstances are very different. Where John Howard was utterly secure for most of his reign, Nelson has been seen from the beginning as something of a stop gap. And while Costello was content to lounge around in his office waiting and hoping for Howard to fall under a bus, Turnbull is already out there buying a fleet of heavy vehicles and giving the drivers Nelson’s address and the route he takes to work.

But the general consensus seems to be that unless Labor wins the Gippsland by-election Nelson will have at least another six months before the party room gives up on him. And by then, who knows? The economy may have hit the wall, Mark Latham may have published the photographs of Brian Burke in bed with half the cabinet or, just possibly, Rudd may have made a few more blunders.

It’s not over yet. Janet may, yet again, have been guilty of premature ejaculation.