Liberal federal Cabinet ministers, backbenchers and hard-heads in the Liberal Party organisation were dismayed and annoyed by the pathetic performance of Treasurer Peter Costello in yesterday’s live debate with Labor’s shadow Treasurer Wayne Swan.

All the pre-debate predictions were that Costello would demolish the lightweight Queenslander who has been Treasury spokesman for a mere 10 months. With more than 11 years as Treasurer and producing 11 federal budgets, Costello entered the contest with formidable qualifications to take Swan apart on all the big economic issues. Instead, he vacillated, prevaricated, droned on and did the smarty pants routine for which he is notorious.

Channel Nine’s worm gave the debate to Swan 56-38. This did not stop Laurie Oakes from disowning the official result delivered by 50 randomly selected swinging voters and calling the debate a draw. The ABC’s Michael Brissenden failed to mention the official 56-38 result and chose to inform 7.30 Report viewers it had been a draw also.

Even if you ignore the worm’s emphatic result, and accept the Oakes-Brissenden call, that amounts to a crushing verdict on Costello’s performance. Called upon to reinforce the government’s major re-election platform – safe handling of the economy – the heir apparent to the prime ministership couldn’t lay a glove on Swan whose previous role before becoming shadow treasurer was shadow minister for family and community services (1998-2004).

Already the Costello worshippers in the media are sweeping the debate under the carpet and trying to pretend it never happened. But the damage has been done: Costello has let down the Coalition at a critical stage in its re-election campaign with a waffling, know-it-all, out-of-touch performance. It will weigh on the minds of Liberal MPs when they come to choose a replacement for John Howard.

One Liberal will, of course, be enjoying Costello’s lacklustre result in the debate – Malcolm Turnbull. But before he can step up to the Liberal leadership contest he has to persuade the voters of Wentworth to re-elect him.