With Julia Gillard on the back foot, Tony Abbott makes a foolish ministry pledge, writes MICHELLE GRATTAN.

A day after Julia Gillard tried to frame her year as neatly as she could with her bold announcement of the September 14 election date, the arrest of MP Craig Thomson threw a heap of mud over the picture.

The Thomson arrest naturally overshadowed Tony Abbott's National Press Club appearance. But the man who is trying this week to cast himself as Mr Positive would have been delighted to find himself upstaged by someone else's negativity.

Thomson has wrought an unbelievable amount of damage on Gillard and her government, and the story keeps going on and on. Not that the ALP can do anything but blame itself. Evidence of his alleged wrongdoing hit the front pages well before the 2010 election but it reselected him regardless. Then, given the new parliament was hung, Thomson became more important than anyone would have anticipated.

So, as the evidence against him mounted, Gillard stuck by him, defending him repeatedly. The ALP helped pay his legal bills. Eventually she and Labor had to distance themselves; Thomson, suspended from the party, went to the crossbench.

If Thomson is convicted, he would be ineligible to be an MP but, assuming he sits tight, the matter is unlikely to be finalised before the election, when he will disappear.

If Thomson departed soon and there was a byelection won by the Liberals, that wouldn't bring down the government, but it would make things more precarious.

The position of - wait for it - former speaker Peter Slipper would become more crucial. Slipper goes before the court this month for allegedly misusing Cabcharges. ''This is a government that relies on the presumption of innocence for its very existence,'' shadow attorney-general George Brandis said.

The government's official stand on Thomson continues its earlier line - that everyone should wait for the law to take its course. But the law is one thing; politics another.

Thomson's facing 150 charges is more bad news for Labor because it reinforces the image of sleaze and corruption that has come out of the Health Services Union affair. The fact that he is on the crossbench is irrelevant. He is, and is seen as, a Labor man.

Gillard is fortunate, however, that there is no sign of the crucial crossbenchers who keep her in power believing Thomson's arrest is something that should affect their attitude. Tasmanian independent Andrew Wilkie said Thomson was innocent until proved guilty and had every right to sit in the Parliament during the legal process.

The opposition is being careful on the presumption of innocence argument but Abbott, questioned at the Press Club, homed in immediately on Gillard, accusing her of ''running a protection racket for Craig Thomson for months and years''.

The sensational Thomson arrest, incidentally, minimised the embarrassment for Abbott of email correspondence that found its way into the media about the preparation of his Thursday speech. His chief press secretary, Andrew Hirst, had advised him not to announce a big cut a Coalition government would make (because it would take off some of the positive gloss).

Abbott told his audience he had rejected Hirst's advice: the undertaking - to scrap the Schoolkids Bonus - was in his speech. It was all a bit strange, however, because the Coalition had earlier indicated the bonus would go - although there had later been some argy-bargy about it.

Apart from confirming this proposed cut, Abbott's address contained nothing new. But in the question-and-answer session he did make an important commitment - and it is an ill-judged one.

He was asked whether he planned to take his whole shadow ministry into an Abbott ministry or would be looking to give portfolios to Arthur Sinodinos (John Howard's former chief of staff who is only a shadow parliamentary secretary), Mal Brough (former federal minister) and Christian Porter (former West Australian treasurer). The latter two will come in at the election.

Emphasising what a good job he believed his team members were doing, Abbott gave this stunning undertaking: ''I think all of them can expect to go into government in their current positions.''

His stand, presumably driven by wanting to keep everyone loyal, is extraordinary - usually an opposition leader is reluctant to give more than a few top people public assurances they will definitely hang on to their same jobs in government.

This is serious foolishness. Abbott has avoided any substantial reshuffle in opposition (beyond minor adjustments forced on him by events). His view is that change produces discontented people, who can be divisive.

But to give carte blanche for them all to keep their areas in government is something else - especially as, if he didn't honour his word, he would be accused of an immediate spectacular broken promise. Depending on the circumstances, that could create bad blood and distrust, which wouldn't be a good start for a new PM.

Abbott does not have the best available team in the right jobs. There is talent on the backbench that should be on the frontbench, and Sinodinos should be in the shadow cabinet. Brough's frontbench claim is questionable given his performance in the Ashby affair, but Porter surely has a case.

It had been assumed that if Abbott won, he would review and improve his line-up. Now he has cut off that option. A leader's authority is usually at its strongest when he or she first takes office; to squander that is rash. Yet if a leader is to be a good PM, having a top team is vital.

His comments will dismay many in his party, not just ambitious up-and-comers wanting jobs for themselves but those looking to promote good administration in government. In all the debate about the opposition's failure to release enough policy detail there has been little attention on how well it would make the transition to government. Abbott's undertaking makes you worry.

Thomson Charged, But Abbott Less Than Arresting