"So every time you make a major statement we have to ask you whether it's carefully prepared and scripted or something on the fly?"

Kerry O'Brien leaned back at this point, a widening of the eyes indicating the first strainings of belief. The backward tilt of the head had the quiet calculation of a toying cobra.

The past week has offered a masterclass in political interrogation. First lesson, that the tempo and tone of the interview needs to be adjusted according to the character of the subject.

Rudd's "mate" moment last week came under provocation, the climax of a mutually belligerent exchange that ended when the PM tipped into either near-homicidal rage or forthright self defence, the difference being in the eye of the beholder.

Last night was different, not so much sweaty sparring as a stern, slightly avuncular, head masterly, chat. Tony would be lured inevitably to his stumbling demise, the interviewer playing on his subject's hope that he could duck what seemed the inevitable Saturday detention, if not a brisk six strokes, if he spoke with apparent candour.

"Seriously, this is a very serious question..." Yes, Kerry it was.

"All of us Kerry when we are in the heat of verbal combat so to speak will sometimes say things that go a little bit further."

Oh dear.

"How are we to know when we're hearing your true position and when you're fudging the truth?"

How indeed?

O'Brien had done more than extract a slip-up on detail, or a fumbled confession. Abbott had gone close to giving the whole game away.

The potency of the moment hangs on the suggestion of a very generally held suspicion: we all know that not all liars are politicians, but we suspect with an increasing sense of certainty (and with the possible exception, at his own insistence, of Anthony Albanese) that all politicians are liars.

And this seems to matter, if the Prime Minister's recent travails in the polls are any guide, Rudd's post CPRS slide in standing having a lot to do with a lingering sense of deception and broken trust.

With Rudd slipping, Abbott presents us all with a neat dilemma: how much more should you trust the politician honest enough to admit that he is at times a liar?

This was worthy of lengthy philosophic inquiry. Instead it brought only the morning's hastily contrived media spectacle, with various Liberal politicians insisting that Abbott had merely given clinching proof of his conviction to honesty, while the last trusted voices in then government - the anti-Rudd tones of Gillard and Tanner - pounced on the specifics of Abbott's admission, that sometimes you could credit what he said, other times not.

Could we trust either side's version?

The answer is probably not. Modern politics, like a piece of impromptu theatre, involves a suspension of disbelief. Tony as good as told us last night.

And it seems the inevitable consequence when politicians, as Abbott said, can only be believed when scripted, if at all. Meantime, the voting public plods on, investing its faith in promises it knows are probably pie crusts. Could this be why when Rudd slumps, Abbott gains nothing? Both houses plagued by this a sense of electoral ennui and disgusted mistrust?

"Most of us know when we're talking to people or when we're listening to people, I think we know when we can put absolute weight on what's being said and when it's just the give and take of standard conversation."

Well no Tony, most of us conduct ourselves in life from a starting point of fairly straightforward sincerity. Our day-to-day conversations are in fact built on trust and simple truth; to behave otherwise is to set life and its relationships on something shakier than a house of cards.

Unless of course you are entrusted, by an honest, hopeful, vote of the people to address the challenges of national government. Or aim to be. Then, it seems, you can lie through your teeth.

Jonathan Green is the editor of The Drum.