The algebra will do the rest to eject NZ First and the Greens from Parliament altogether.
Such confidence is the context for Bridges' announcement on Monday that there will be no new taxes under a Government he leads.
Labour, the theory goes, will soon be saddled with Tax Working Group (TWG) recommendations that are both politically unpalatable and raise serious implementation questions.
Every capital gain, except for the family home and the land beneath it, is to be taxed on realisation at the normal income tax rate, including every KiwiSaver account, share portfolio, privately-owned business and rental property.
For assets without active secondary markets, some form of baseline valuation will be needed on a set valuation day.
The stakes will be high. Currently, if CVs are too high or low, we can hope higher rates in the short run might be balanced by a marginally higher price on sale, or vice versa.
Under the proposed CGT regime, CVs will have much greater significance. Too low risks owners losing a big hunk of their sale price to the IRD. Too high and they can look forward to a tax rebate on sale.
For SMEs, the problems are even worse. How is every fish 'n' chip shop to be valued on valuation day?
Sir Michael Cullen's insistence that the IRD won't care too much as long as the initial valuation is "reasonably fair" seems at odds with the experiences of those whose affairs have come under its microscope.
Labour, National hopes, will either have to adopt a controversial TWG proposal or go into 2020 with no clear tax policy, allowing National's advertising agency to make one up for them.
Bridges' promise to repeal fuel taxes, any CGT and introduce no other new taxes in his first term gets him ahead of this game. But Bridges' pledge comes with the cost of narrowing his policy options for 2020.
A case can be made that the current tax regime disincentivises the two things New Zealand needs more of, namely, higher profits and wages.
While the Lange and Key Governments readjusted that when introducing GST in 1986 and shifting the balance further in 2010, collecting GST now involves an arguably losing battle with technology.
Maybe new options should be considered.
Similarly, there is an argument for a carbon tax instead of the failed emissions trading scheme, especially now only the most swivel-eyed environmental economist still believes the world will ever adopt a comprehensive carbon trading system.
For Auckland transport, regressive petrol taxes should surely be replaced by a modern GPS-based congestion charging system.
Unless Bridges' pledge is interpreted as meaning only that the total tax burden will remain the same or lower as a percentage of GDP, he seems to have taken all such ideas off the table. This is probably the correct electoral judgement.
Since the first MMP election in 1996, New Zealanders have a record of voting for the least innovative policy programme. For all the rhetoric about knowledge waves, economic transformation, step changes, brighter futures and being ambitious for New Zealand, Helen Clark, John Key and now Ardern have gone out of their way to avoid alarming anyone.
The result has been New Zealand's living standard declining relative to much of the rest of the world.
Bridges may be right that simply offering a fourth term of the Key-English regime, or even a second term of Ardern's, is his best path to power, but it also comes with a commitment not to seriously address New Zealand's ongoing journey out of the First World.
Even electorally, Bridges lacks the personal connection of Ardern, Key or even Clark in her prime. It's difficult to see how he can compete with Ardern's smile-and-wave and lightweight pitch with a bland, steady-as-she-goes appeal.
- Matthew Hooton is managing director of PR and corporate affairs firm Exceltium.
