Three years ago, Julia Gillard took what she believed was a decision about mere language - whether a new carbon price to be set by government was technically a tax or a charge.
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Introducing a possible 'deficit tax' would not break an election promise of no new taxes, says Tony Abbott. But what constitutes a broken promise in the mind of the Prime Minister?
It turned out to be utterly crucial and ultimately killed her leadership.
Having heroically decided on a fixed carbon price period, Gillard wanted no quibbling on the language.
Despite declaring "there will be no carbon tax under the government I lead" before the election, she decided not only to go with the carbon price, but to accept up-front that it was to operate like a tax.
She would cop the criticism on the language before moving on to the more productive argument over the policy's substance, which she believed she could win.
It was a fatal political mistake. Tony Abbott ensured the debate never moved to that next stage.
Notwithstanding majority public support for action on global warming, the substantive policy debate was never allowed to re-ignite because Abbott ensured it stayed focused on deceit - on Gillard's breach of trust.
Counterpointing Gillard's "honesty" problem, Abbott's double-pledge was that he would keep all of his promises including that there would be no carbon tax and no new taxes. He recently labelled Labor's trust problem a "quagmire" and one into which he would never stray.
And yet here he is today, not even a year on the clock or a first budget under his belt, and these central pledges are hanging by a thread.
Voters know what was said because it was repeated so often - no new taxes, no broken promises, no surprises, no excuses.
They will now be measuring these unqualified statements against his words on Melbourne radio on Tuesday as a pre-justification for a deficit levy: "We do have a short-term problem and we do need to deal with it," he told 3AW.
Abbott is asking for the kind of understanding from voters that he did so much to deny the previous government.
"I think if there was a permanent increase in taxation that would certainly be inconsistent with the sort of things that were said before the election.
"We want taxes going down not going up, but when you're in a difficult position, sometimes there needs to be some short-term pain for some long-term gain."
Debt tax not a broken election promise?
Prime Minister Tony Abbott says a debt tax on higher income earners would not be a broken pre-election promise as it would be a temporary measure. Nine News.
Let's be clear. Abbott is asking for the kind of understanding from voters that he did so much to deny the previous government.
Worse, he is playing word games when it is abundantly clear that the "levy" being considered, is a tax, plain and simple. Far more so, incidentally, than the fixed price per tonne on carbon pollution.
Going to the substance of the levy, it is arguable that it is worth considering because there is a revenue shortfall and there is a need for expenditure and taxation to be re-aligned. That is, for both spending to brought down and taxation increased.
But as to the claim of an emergency or a crisis, that is not supported by the facts.
Either way, by his own test, Abbott may have surrendered the right to have that substance debated.