The 2016 federal election will be won and lost in the centre, from which Bill Shorten seems to be exiting at speed to make way for a rampaging Malcolm Turnbull, writes Paula Matthewson.

Despite its lofty principles, politics at its most basic is a battle in the electoral marketplace of product A against product B.

Some voters scrutinise the label (policies) before selecting a product (party or politician) on election day. Some choose the product they think will be kindest on their budget, while others go for the most attractive packaging. There are voters so loyal that they'd never contemplate a change from their current brand. And yet there are others who like to mix it up, selecting a different product at each election.

As a result, political strategists strive to find ways to differentiate their product/party/politician from the rest - to make their product stand out and be reassuringly familiar to loyal customers while also presenting an alternative for those potentially looking for a change.

This differentiation strategy worked reasonably well for Bill Shorten when Tony Abbott was prime minister. Presented with the choice between the increasingly belligerent prime minister and the slightly goofy but mostly harmless Opposition Leader, and voters unsurprisingly favoured the innocuous option.

However, Shorten's strongest selling point was that he wasn't Abbott. Unfortunately for him, the Labor alternative suddenly became less attractive to voters once the Liberal product was upgraded to Turnbull 2.0.

At this early stage, Turnbull also is benefiting from product differentiation. Shorten amusingly pointed out this past week that he "shares in the national relief that Abbott is no longer prime minister" that undoubtedly is reflected in the new PM's stellar opinion poll ratings.

Clearly conscious of the need to be more than not-Abbott, Turnbull has charted a perilous course between the firm commitments he gave conservative Liberals and Nationals when he became leader, and the progressive expectations of the voters that he also needs to retain government.

As a result Turnbull has maintained Abbott's firm line on combating terrorism - albeit with more inclusive, less inflammatory language - while decrying the need to be hairy-chested. And he's continued to justify the use of offshore detention to deter boat-borne asylum seekers, while scrapping some of Abbott's sops to the right such as the ill-considered reintroduction of knighthoods.

Ultimately, Turnbull won't allay suspicions that he's Abbott in a nicer suit until he and the Treasurer Scott Morrison hand down their first federal budget. As we learned before the first Abbott/Hockey budget, it's one thing to talk about fairness and quite another to produce a fair budget.

Shorten's differentiation challenge is different altogether. In the past Labor stuck fast to PM Abbott on national security issues such as terrorism and asylum seekers but was able to provide a contrast to the Coalition on progressive issues, as well as economic fairness and being in touch with voters' everyday concerns.

If Turnbull and Morrison deliver a budget that is not only fair but also seen to be so, Shorten is left with the choice of differentiating himself from Turnbull on national security or progressive issues.

Either option is as fraught for Shorten as Turnbull's delicate dance between his own party's conservatives and moderates. With the Australian community in a state of high anxiety over national security - and despite the dubious connection between terrorism and asylum seekers - the Labor leader knows he can't afford to be seen to go soft on either.

That leaves the leader of the ostensibly progressive Labor Party to grapple for the left-of-centre vote with the ostensibly progressive leader of the Liberal Party. In order to differentiate himself from Turnbull as the PM shuffles leftwards to the centre of the political spectrum, Shorten is forced to move further left and into what is traditionally the Greens' territory.

As a result, voters are now presented with a Labor Party that seems to have adopted a caricature of the Greens' agenda - whacking high-income earners, demonising multinationals, taking a nanny-state approach and adopting an overly-ambitious environmental agenda.

Interestingly, as the Coalition has gained in the opinion polls since Turnbull's return, the Greens' vote has remained relatively unchanged. This suggests soft Labor voters have shifted to the Coalition, while soft Green voters have not (yet) been persuaded to change to the Shorten's Green-lite Labor.

Even more concerning for Shorten is the news that Turnbull's return to the Liberal leadership has increased the number of undecided union members by almost 10 per cent. According to the ACTU, this has "been at the expense of soft progressive voters", meaning the Labor movement would be "targeting all previously identified 'soft Labor' and 'soft Greens' voters in (their) persuasion efforts".

It may make sense for Labor to take on a greenish tinge, given that a number of their key Opposition MPs are at risk of losing their seats to Green candidates at the next election. However, the 2016 federal election will be won and lost in the centre, from which Bill Shorten seems to be exiting at speed to make way for a rampaging Malcolm Turnbull.

Paula Matthewson is a freelance communications adviser and corporate writer. She was media advisor to John Howard in the early 1990s. She tweets and blogs as @Drag0nista.