Because Mr Shorten appears determined to win the keys to The Lodge by actively campaigning on policy areas closest to his rival’s heart – and even taking his rival’s position.

Such is the strange nature of federal politics at present that Malcolm Turnbull’s best chance of retaining the support of his conservative backbench [which he must do to retain the party leadership] is to publicly prosecute the case for a number of policies that contradict his personal views.

And Mr Shorten is taking great delight in making life as uncomfortable as he possibly can for the PM.

First it was same-sex marriage.

Mr Turnbull has long been acknowledged as a strong supporter of same-sex marriage and his elevation to the Liberal leadership gave hope to many same-sex marriage supporters that change might be imminent.

Sadly, that proved not to be the case as Mr Turnbull put his political ambitions ahead of his personal beliefs by toeing the party line that a costly, divisive and pointless plebiscite should be the first step towards legalising same-sex marriage and bringing Australia into line with much of the western world.

Now Mr Shorten is targeting Mr Turnbull’s past presidency of the Australian Republic Movement by promising a referendum on becoming a republic during Labor’s first term in government.

Of course, becoming a republic – unlike legalising same-sex marriage – requires constitutional change and can only be done through a referendum, so commentators who have claimed some sort of inconsistency in Mr Shorten’s support of a referendum while opposing a same-sex marriage plebiscite are way off the mark.

And while becoming a republic has always been a Labor policy position, it may not have been put back in the political spotlight had it not been for the difficult situation it creates for Mr Turnbull.

The danger for Labor, though, is that credible opposition must do more in the long run than simply make the PM squirm.

It’s not enough to push only those policies that wedge the opposition – Labor must start to convince the public that Mr Shorten is a viable alternative as prime minister.

And regular polls that show he is still trailing Mr Turnbull as preferred prime minister show there is still a lot of work to be done on that front.