But the Opposition Leader, Tony Abbott, doesn't care whether there is a ''smoking gun'' or not because his strategy is to badger the PM, until there is doubt in the community.

Simply put, if you throw enough mud, some will stick.

But here's the thing - in Parliament on Monday, he didn't lift a shovel.

He left the ''muck-raking'' to his deputy, Julie Bishop, who had various documents to back her questions.

The opposition's strategy allowed Gillard to display the contempt in which she holds Abbott - and the confidence she can ride out this row - by noting at the end of Question Time for those listening on radio that the Opposition Leader was actually present.

The jab about his seeming invisibility came after every question from the opposition was posed by Bishop and every one of her questions was to the PM about the slush fund row.

The opposition can claim some success in forcing the PM to talk about the events of so many years ago when she was deceived by her then boyfriend, union official Bruce Wilson.

This is a significant advance because the PM has been batting away questions in Parliament by instructing the opposition to read the transcript of her press conference in August, the one that was supposed to kill off the specuation.

Moments before Question Time, she gave a second lengthy press conference on the issue, in which the PM challenged the opposition and the media to weigh her credibility against union ''bagman'' Ralph Blewitt who has returned to Australia, appparently with the specific intention of undermining the PM. Gillard's decision to take more media questions was designed to take some heat out of the opposition's attack, which had been well advertised.

She is concerned the issue will dominate this final sitting week of Parliament and, in turn, encourage the wacky conspiracy theorists to feed the rumour mill over the summer break.

This is a legitimate concern for the Labor government, trying to build public support for an election which is now less than 12 months away. If the issue keeps bubbling, even without any visible foundations, the notion could build in the court of public opinion that there ''must be something there''.

Otherwise, a punter could ask, why would the media and the opposition continue to pursue it?

And why do the same questions keep surfacing if the PM has already answered them?

Here's the PM's answer to a key question: she did not report alleged wrongdoings by her then boyfriend to the police or the union in 1995 because she did not know it. She had given Wilson legal advice about the incorporation of a legal entity for the union but that's where her involvement started and finished - she did not know anything about the bank accounts.

However the opposition will pursue why she was not so definite on whether $5000 had been deposited into her bank account, or why she had to consult receipts before declaring she had paid for all the renovations to her house.

Gillard's performance was confident and steely. She's had enough of the frustrating ''smear'' campaign but now it's up to the Coalition to decide whether to plough on through the mud.

Ross Peake is Political Editor

Twitter: rosspeakeCT