Bill Shorten and his Parliamentary Labor colleagues would have realised very early on in Malcolm Turnbull's prime ministership that Labor's poll numbers were destined to decay. The only relevant consideration for the ALP back on September 14 was how low the numbers might plumb before Mr Turnbull's honeymoon ended and/or Mr Shorten began making an impression in the policy or parliamentary spheres.

Neither of those two scenarios has yet eventuated, and the latest Fairfax/Ipsos monthly poll indicates Mr Shorten's rating as preferred prime minister is now 18 per cent, down from 21 per cent in October, and 39 per cent in August – when the unpopular Tony Abbott was still prime minister. Labor now trails the government by 56 per cent to 44 per cent on a two-party preferred basis, having led it 54 per cent to 46 per cent in August.

Editorial

Two months of poor polling don't presage electoral disaster for Labor, and every prime minister who's ever enjoyed stratospheric popularity levels (Mr Turnbull's approval ratings are 69 per cent) eventually falls back to earth. But with indications the electorate has stopped listening to Mr Shorten, there's no immediate prospect that his voter appeal can be burnished further.

The Fairfax/Ipsos poll (specifically that part of it probing voters' reaction to a GST increase) represents further bad news for Mr Shorten in that it suggests a majority of voters support an increase if it includes compensation for lower and middle income earners. Federal Labor's view that there was electoral mileage in opposing a GST hike (even as state Labor premiers like Daniel Andrews softened their initial opposition) now looks like a serious miscalculation.

That strategy seems to have been borne of a belief that Mr Shorten could out-point Mr Turnbull in a public debate – a not entirely implausible idea given his "success" against Mr Abbott. Mr Shorten is a competent communicator, but it's arguable he was made to look something better than that by Mr Abbott's own verbal fumbling. By contrast, Mr Turnbull's own advocacy skills are far superior. Indeed, the ease with which Mr Turnbull discusses politics, ideas and matters of state (as opposed to his predecessor) may well further explain why voters have warmed to him.

Mr Shorten is now in the awkward position of trying to remove some of Mr Turnbull's gloss while simultaneously advocating policies that demonstrate to voters Labor's fitness to govern – and all in less than a year. His "exoneration" in the Royal Commission into Trade Union Governance and Corruption will help, though arguably the experience has solidified the public image of him as both a creation of and a creature of the union movement.

The leadership of Simon Crean (another union man) foundered after just two years – largely as a result of uninspiring rhetoric. Mr Shorten's poll numbers are now approaching those of Mr Crean at his most unpopular, and though it's much harder now for the Labor party to oust leaders mid-term, he wouldn't want to test their resolve with more polling like this.