"Visiting Queanbeyan today, Mr Rudd was asked by a journalist to name the tax rates and where thresholds kick in.And it is.
Mr Rudd replied: "Well, as of July 1, if you went through the four thresholds, I think the high threshold kicks in I think at $175,000, then I think it cascades down the spectrum.''
Mr Costello seized on the blunder, attacking Mr Rudd in parliament and pressing him to release Labor's tax policy.
"He couldn't name a single rate, he couldn't name a single threshold, and the one threshold that he named of $175,000 ... just doesn't exist,'' Mr Costello told parliament.
"Since the Labor Party demands an election to be called on a daily basis, you would think they might have the decency of releasing a policy so that people can know what it is.''
Mr Costello said tax thresholds don't cascade.
"Cascade is a form of beer, it is not a form of tax threshold.
"This would be amusing if it were not serious.''
This isn't a cheap shot, like asking a pollie if they know the price of bread (they don't, why bother asking).
In my living memory there has never been a tax rate that cuts in at the likes of $175 K. Ever. The highest tax rate has always been applied at a much lower income level.
Let's spell this out: Rudd is 54 years old (or thereabouts?). I would expect most people of that age, politician or not, to have some clue about tax rates. Of a politician, I would expect them to not only know about current tax rates, but to also have significant knowledge and understanding of the history of taxation practices in this country. Rudd clearly knows neither.
(I wonder what he believes the average income to be?)
This is the man who is going to be our next Prime Minister?
Okay, the top tax rate currently cuts in at $150 K and from 01 July 2008 this will rise to $180 K.
The ALP have gone straight for the tit-for-tat (as you do), releasing a Howard tax gaffe from sometime back in parliament - don't know what those details are.
Meanwhile, Rudd has been forced to go public with an old health matter after details were "leaked" to Channel 9.
"The man who would be PM revealed last night that, about 15 years ago, he had an operation to replace his aortic valve with one from another person.
He said the faulty valve was caused by childhood rheumatic fever, that the operation was "a standard procedure" and he'd been "fit as a fiddle ever since".
As much as the leak allegedly comes from Liberal sources or supporters, the Libs won't run with this, so the matter will vanish quickly. It wouldn't surprise me to see a lot more of this type of thing: run something up the flag poll; pull it straight down again.
If Rudd persists with being a "small target", building a portfolio of small doubts, concerns and irritants, hoping that the cumulative effect is sufficiently corrosive, is probably a reasonable tactic from the Libs. Besides, they don't seem to having anything bigger to work with right now.