Richard Nixon declared certain of his statements inoperative. George Bush sometimes misspoke. John Howard had his core and non-core promises. And Winston Churchill admitted occasionally being guilty of a terminological inexactitude.

Now Tony Abbott has taken his rightful place in this pantheon of weasel-worded mendacity by confessing that some of his policy pronouncements are not entirely consistent. What he says in the heat of the moment should not always be taken with the same degree of assurance as what he reads from carefully scripted documents.

Or something like that. As his attempts to explain his position to an incredulous Kerry O’Brien continued, he became Jesuitical to the point of incomprehensibility. It was not, as he agreed later in a moment of indisputable candour, his finest interview.

And the real stupidity of it was that all he really had to do was to say that he had changed his mind; that the weight of evidence had persuaded him that the need for a comprehensive, firmly funded system of parental care was sufficiently urgent for him to abandon his earlier ritual pledge of no new taxes. Red Kezza would still have given him a working over, but at least he would not have been lumbered with Phoney Tony for the rest of his career, and he would not have been subject to the harassing he is going to get from government and media alike every time he says anything purportedly serious from now on.

And, of course, he would not have had the embarrassment of Barnaby Joyce trying to help him out: “What someone might say to their lover in the heat of passion should be entirely different to what you would say to the lady checking out your groceries at the supermarket.” Oh, I don’t know: “Do you take American Express?” would seem to cover both situations.

But moving on, it became instantly obvious that assessing Abbott’s credibility on any given occasion was going to be even more difficult than he had suggested. Reading from his carefully scripted Budget reply speech the previous week, he had stated — even promised — that the opposition’s proposed spending cuts would be fully detailed by Joe Hockey at the Press Club.

Nothing heat-of-the-moment about it: this was a serious and considered commitment. Or so the prima donnas of the press gallery believed when they fronted on Wednesday, only to find that Hockey had flick-passed the commitment to Andrew Robb. He blandly announced a grand total of $46.7 billion and went on to give a talk on what he somewhat grandiosely described as his economic philosophy.

The hacks took this as a serious affront, and unanimously decided that Hockey’s failure to deliver was the real story; what he actually had to say was no longer relevant. Robb did belatedly appear to hand out a list of proposed savings, and to answer a few questions, but the news coverage centred around Abbott’s and Hockey’s unforgivable snubbing of the people who really run things in Canberra.

And the anger set the tone for what serious coverage there was: Robb’s list was derided as ill-informed and misleading, in that it consisted largely of axing proposals that were not even on the drawing board, yet alone actually costing money, like the proposed cuts in company tax, and in selling off capital assets such as Medicare Private. Even many of the current programs that would be axed, like the Building Education Revolution, would be replaced by others in the same field that could, as Robb proudly admitted, be even more expensive.

Independent economists estimated the total real savings as somewhere between $5 billion and $8 billion, which did not even cover the cost of new coalition promises already announced; even if Lindsay Tanner’s estimate of $15.7 billion is an exaggeration, items such as Abbott’s direct action on climate change won’t come cheap. The Australian, as always, tried to do its bit: under Hockey’s headline figure of $46.7 billion it published a list of everything that could conceivably be regarded as a saving and quite a few things that couldn’t. Even so, the total only came to $42.6 billion — but hey, what’s a few billion between close friends?

Perhaps there are a few more candidates for Julia Gillard’s NAPLAN numeracy tests. Or perhaps the list just wasn’t very well scripted. It seems likely that Merry Andrew will join Phoney Tony and Sloppy Joe in the Labor lexicon of economic shadow ministers who cannot be taken seriously. It might be time to bring Malcolm Turnbull back into the fold; at least he knows something about money.

This is obviously one area of vulnerability for the coalition; another is that they are rapidly painting themselves into a corner over what Abbott continues, gratingly, to call Rudd’s Great Big New Tax. The miners’ public opposition is vigorous and unremitting, but behind the scenes a lot of negotiating is going on and the government is getting some high-powered support from Ken Henry in Treasury, whose defence of the tax was comprehensive and passionate, and from Ross Garnaut, arguably the country’s most respected economic planner, who described it as elegant, if badly sold and in need of the odd tweak. GetUp’s supportive advertising campaign isn’t hurting either.

Most of the hard heads accept that some sort of resources rent tax is inevitable; the only question is how much ground is the government prepared to give. Almost certainly the answer is not much; the political imperative is not to be seen to be backing down in the face of threats and bluster based on pure self interest. It is more likely than not that an agreement will emerge before the election, and that it will be one that can and will be portrayed as a win for the government. Which will leave Abbott, yet again, without a central issue.

To be consistent, he should continue to oppose what will still be a great big new tax on mining industry, even if it ends up being in a form that the industry accepts. But as last week demonstrated conclusively, Abbott has never been obsessively concerned with consistency.