PM's unfortunate jibe has come back to bite him, big time.
As much as Bill English downplayed yesterday's downgrades of New Zealand's credit rating, the double whammy from Standard & Poor's and the Fitch ratings agency inevitably casts a big shadow over National's claim to be the most competent manager of the economy.
Coming so close to an election, the downgrade is a huge psychological fillip for a Labour Party desperate to realign the debate on economic management on its terms.
Labour has been arguing - with some justification - that National has not made the hard decisions needed to address imbalances in the economy such as the mountain of private debt.
On that score, the chickens have certainly come home to roost for National in the form of the rating downgrades.
John Key's unfortunate talk of "muddling through" the fallout from the international debt crisis has come back to bite him, big time.
Labour is right.
While National has remodelled the tax system, it has refused to confront issues such as raising the age of eligibility for superannuation - something Standard & Poor's tacitly noted.
National has instead weakened savings mechanisms such as KiwiSaver and the Cullen superannuation fund. National might argue otherwise, but selling chunks of state-owned companies and chopping back the public service do not add up to be solutions to New Zealand's economic woes.
In contrast, Labour is walking its talk. With its capital gains tax and a yet-to-be-announced savings policy which may well contain some stick - in the form of compulsion - as well as some carrot, Labour is at least addressing the areas where the hard decisions will have to be made.
It could be argued that Labour's shocking poll ratings leave it little option but to take risks and moot radical policy positions.
Were the gap in the polls between the two major parties much narrower, Labour might not have been so adventurous.
The problem for Labour before yesterday was that voters did not seem to think there was a problem to solve. National had skilfully played to that mood by saying New Zealand was better placed than most countries to ride out - or muddle through - the impact on exports and so forth from any international downturn resulting from European and American debt crises.
No doubt every Finance Minister in the world - Greece excepted - uses the phrase "better placed". Wayne Swan in Australia certainly does.
The rating agencies, however, clearly are not so sure about New Zealand being "better placed" at all.
Labour's frustration at what it saw as National's "sedating" of voters as to the true fragility of the economy has been evident in a curious parliamentary sideshow in recent weeks run by David Cunliffe, Labour's finance spokesman, and Stuart Nash, the party's revenue spokesman.
Their gambit had involved putting questions to English covering the rise or fall of a highly selective bunch of economic indicators during the term of the minority National Government. Those figures covered the years and months National has been in power. They thus purported to show National's track record on the economy. Taken in isolation, figures showing economic growth going backwards and Government borrowing going skywards do not reflect well on National. However, measures of economic performance cannot be taken in isolation. It is absurd to assess a Government's performance without taking into account outside influences such as international commodity prices and the sometimes lengthy time lags before some indicators such as the rate of unemployment start to shift.
On top of that, the Treasury's fiscal update before the last election (when Labour was still in power) scaled back growth forecasts and projected that Budget surpluses would rapidly turn into deficits as a result of the-then global financial crisis.
English has looked rather bemused when Labour has played this little game.
To anyone with the faintest knowledge of recent economic history, this crude attempt to undermine the credibility of English and Key as economic managers has been laughable.
English must have been asking himself why two supremely intelligent members of Labour's team were bothering to risk making such fools of themselves.
What they were doing was trying to ensure Labour is a leading participant in what is shaping as the major issue of the election - economic management.
If Labour is shut out of that debate, it will be shut out of the election.
The party is already handicapped by the refusal of voters to connect with Phil Goff.
While voters are unhappy about issues such as the cost of living, they have low expectations of what politicians are able to do about it.
This is why Labour's attempt to steer the economic debate through the promotion of a capital gains tax failed. While the arguments favouring such a measure are strong, the electorate was simply not on the same wave length as Labour when it comes to the need for one.
This forced Labour to concentrate on running down National's performance as economic manager - even if that requires taking a few liberties in doing so and rewriting economic history.
Such revisionism may seem silly to those who participate in or closely watch the debate on economic policy.
But that was of little worry to Labour.
What the party was relying on was the short memories of the many more voters who are not part of that debate.
Labour was also relying on the theory that explaining is losing - that National's countering of an outrageous claim would have far less impact than the claim.
The credit rating downgrades make that warped strategy far less necessary. They should also serve as a wake-up call to the wider New Zealand electorate that merely muddling through is not good enough.
The blowtorch is now on National. It can no longer cruise through the election campaign. It is going to have to come up with answers to satisfy the ratings agencies.
And they are not answers which are going to be all that popular.