Given the head of the union royal commission used to be an eminent judge, Dyson Heydon might have initially thought it would be easy to decide whether or not he should continue to preside over the inquiry into union corruption.

Surely it was only a matter of weighing up the evidence in light of any similar legal decisions, and making an objective assessment?

With two deadlines lapsed, it now appears Justice Heydon has realised the task is a little more complicated.

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Labor leader Bill Shorten emerged unscathed from his interrogation – for now. Photo: AAP

A day before he was due to bring down the ruling, the former judge advised it is going to take a bit longer to make a decision whether or not to sack himself.

Even more curiously, Justice Heydon hasn’t named a date on which the decision will be announced; instead his media release essentially advised interested parties to “watch this space”.

This leaves not only the royal commission and the unions hanging in suspense, but also the political pundits who’ve been closely monitoring developments. Justice Heydon’s self-performance review is fascinating because the decision could have an impact on the electoral prospects of both Tony Abbott and Bill Shorten.

The consequences for Mr Shorten are perhaps most obvious. If the former union leader was found by the inquiry to have been involved in corrupt behaviour or acted against the interests of his union members, the Labor leader would be a political dead duck.

So far, the royal commission has found nothing on the Opposition Leader that is definitively incriminating.

Mr Shorten certainly did face uncomfortable questions during his two-day appearance at the inquiry. One line of interrogation divulged that his campaign manager at the time was “donated” by a labour hire company that was also involved in wage negotiations with Mr Shorten’s union.

However, Mr Shorten handled the questions well enough, even though he obfuscated on a number of occasions.

This dancing around eventually prompted Justice Heydon to chastise the Labor leader for his “extraneous” answers, noting such un-responsiveness could damage Mr Shorten’s “credibility as a witness”.

Labor and the unions took particular note of Justice Heydon’s intervention. It appeared to confirm the union royal commission’s suspected purpose: to undermine voter trust in the Labor Party by its close association with the union movement, which the Government hoped would be exposed as riddled with corruption.

PM Tony Abbott still trails in opinion polls. Photo: AAP

So when it emerged that Justice Heydon had links to the Liberal Party, and even a long association with the Prime Minister, Labor and the unions pounced on his perceived bias as a way to shut down the inquiry.

According to at least one legal opinion, if Justice Heydon goes, so does the royal commission.

It could be argued that much of the inquiry’s work has been done. Dodgy behaviour has been exposed in several unions, and the royal commission has referred a number of people to the Director of Public Prosecutions to consider legal action.

However, the Prime Minister has already indicated the royal commission will go ahead – with or without Justice Heydon.

The invitation to Wednesday’s Liberal Party fundraiser that landed Dyson Heydon in hot water.

This is because Mr Abbott has as much at stake in retaining the union witch-hunt as Mr Shorten has in killing it off.

Try as he may, the Prime Minister has proved incapable of returning the Coalition to an election-winning position. He tried to lure voters back to the government with a magic pudding budget, and when that didn’t work he tried to scare them back with bogeyman stories about terrorism, asylum seekers and the ABC.

Yet the opinion polls remain steadfastly with Labor in an election-winning position; as it has been since late 2013.

Mr Abbott therefore needs the royal commission to bring down, or at least seriously damage, Mr Shorten in the hope of making Labor untrustworthy in the eyes of voters. The PM believes that if he can close the opinion poll gap between the Government and the Opposition, an election win will be within his grasp.

If the commissioner declines to step down, Labor and the union movement have an interesting question to ponder – do they continue to cooperate, or boycott the proceedings and be represented as having something to hide?

And if Justice Heydon were to sack himself, Mr Abbott would have to justify the expense of re-establishing the inquiry with a new royal commissioner who would essentially have to start from scratch.

Mr Abbott and Mr Shorten will be hoping the commissioner brings more wisdom to this decision than he did when he accepted that speaking invitation.

* Paula Matthewson was media adviser to John Howard in the early 1990s and then worked for almost 25 years in communication, political and industry advocacy roles. She is now a freelance writer and communication strategist. Paula has been tweeting and blogging about politics, the media and social media since 2009 under the pen name @Drag0nista.

Read more columns by Paula Matthewson here