Why would he want to become deputy-PM anyway? Treasurer and Foreign Minister are far more powerful cabinet positions.

Because Downer can no longer jump over Peter Costello and succeed Howard. He has been positioning himself for the run to the top in the post Howard era of late.

Cameron - Foreign Minister is arguably not usually regarded as a powerful Cabinet position (senior, yes...) because the constituency is not Australian (except for consular cases). And Deputy PM will always be a National party spot until either that party or the Coalition agreement impodes. For a good take on Howard and AWB, Pryor in the Canberra Times offers his usual brilliance.

Phil, After PM and Treasurer, the Foreign Minister is the next most "in the news" politician. Turnball got shafted for this reason, not only is he subject to cabinet discipline now, his new position is largely unnewsworthy. Australia is an international global trading nation which means the foreign minister has one of the highest media profiles. I don't see how wanting to be deputy PM will increase that. Maybe is he hoping the PM will kark it? But that is hardly a political strategy.

Cameron,
what you say is true. Downer is definitely inner circle in the Howard Government ---one of the top three (eg., Howard, Ruddock, Downer) in terms of the neo-conservative strategy to stay in power.

But it is also true that Downer had been making moves to increase his seniority rankings now that Abbott has drifted away

Those moves--atempts to get his own people through preselections for safe seats--- can only mean he fancies himself for the top job when Howard goes. There's political ambition--power drives them. It's what Canberra is all about--- the logic of power.

Michelle Grattin has a good article in The Sunday Age on the ministerial issue:

If we take the ministers' word that they did not know of the bribes, then the question becomes whether they did enough to investigate the allegations of them.

At the end of all the evidence this will be a matter for judgement — first Cole's and then that of politicians and the public.
She adds that the issue has become whether ministers "turned a blind eye" as Labor says, or fell victim — because they were gullible — to AWB deception.

This remains unclear and that is why it is important the ministers (and this should include Howard too) face the commission, which is out of their comfort zone.