If you had any doubts that Joe Hockey would be an absolute disaster as Opposition Leader, yesterday should have dispelled them.

There’s something weird going on in the Liberal Party at the moment, whereby if you perform diligently and competently in your portfolio, you are left to labour in obscurity. But if you either ignore your portfolio in favour of offering a running commentary on your own party, like Tony Abbott, or you fail to use regular opportunities to land some blows on your opposite number in an important portfolio like Health — that’s Peter Dutton — you get spoken of as a possible leader.

And if you’ve made a hash of a critical portfolio like Treasury, you get sounded out to step into the top job.

Joe Hockey has had two goods ideas as shadow Treasurer: a Public Register of Government Borrowings, which he negotiated for Wayne Swan to take up, and breathing life into the non-bank mortgage market via guarantees for appropriately-graded securities. The rest of his tenure has been a shocker. From bagging the G20 and Barack Obama, to saying low interest rates were more important than jobs, to prematurely committing the Coalition to hacking Government spending back to 24% of GDP — a position today repudiated by Malcolm Turnbull — Hockey has shown a disposition to open his mouth first and think later.

Much of the business community regards him as, not to put too fine a point on it, a clown. They may disagree with Malcolm Turnbull’s economic policies, and think he is disposed to the occasional brain-snap, but they know he is a figure of substance, and always has been.

Hockey is an amiable lightweight at best.

And he displayed that again yesterday when he was asked by Neil Mitchell whether he’d been sounded out for the leadership.

“I am not going to lie and pretend something hasn’t happened,” was Hockey’s reply. At best it was naive. At worst, it looked like deliberate destabilisation cloaked in sanctimony. Nothing could have been more calculated to add to the Coalition’s turmoil engendered by the pitched battle over the Government’s CPRS. Nothing.

For a start, Hockey could have lied. Or he could have declined to answer the question, declared “I’m not going to talk about the leadership.” But no, he had to throw some petrol on the fire that is consuming Malcolm Turnbull’s leadership.

The turmoil within the Liberals has come about for two reasons. Malcolm Turnbull’s brain-snap last week in lashing out at his critics was the immediate cause, but that was merely the product of the incessant sniping that has broken out since Andrew Robb took time off. Ian Macfarlane has calmly and sensibly gone about his job of crafting the CPRS amendments, but the absence of Robb has given their opponents licence to break cover and try to overturn shadow Cabinet’s decision to negotiate an end to the havoc emissions trading is wreaking on the Coalition.

The Liberals, and for that matter anyone who wants a functional Opposition — which should be the rest of us — need Andrew Robb back on deck as soon as possible to start righting what is a badly-listing vessel. If Malcolm Turnbull survives, he needs Robb, preferably in the shadow Treasurership, to try to give some much-needed substance to the Coalition’s economic credentials, and start restoring the Opposition’s standing with the business community, especially in Melbourne, where Joe Hockey is not as well-known as he is in Sydney. Quite how Turnbull and Hockey are going to elicit strong financial support from their traditional donor base in the lead-up to the next election is a mystery.

The promotion of Robb won’t happen, of course, given Hockey now has leadership-rival status and any move would be seen as a demotion. Like Julie Bishop, the Liberals are stuck with an underperformer in a senior position. The only way to fix the problem of Hockey’s underperformance is to promote him. And anyway Robb, of course, remains ill. He has perhaps wisely dealt himself out of the current turmoil. His office says he is “unavailable” for at least a week.

The departure of Peter Costello also focuses attention on another aspect of the leadership turmoil. There has not been a Victorian leader of the Liberal Party since the end of the 1980s, in the dapper form of Andrew Peacock. The rest have been from Sydney, excepting Alexander Downer, and the two post-Turnbull candidates currently being mooted are both from Sydney as well. Costello is said to have been busy promoting Hockey as a suitable replacement for Turnbull.

In the event that a majority of Liberals decide that Turnbull is no longer viable, replacing him with another Sydney moderate, in the form of Hockey, or an arch-conservative like Abbott, is unlikely to solve the party’s deep internal divisions. But Andrew Robb, once he recovers his health, might.