As one senior journalist tweeted this week, "National needs to either detail what govt spending it would cut, or stop going on about it."
So what's going on here?
The explanation, as it so often is in politics, is polling.
A recent survey by Talbot-Mills Research, released to their corporate clients, showed that Kiwis back investing in health, housing and education over reducing spending and debt and do so by a ratio of nearly two to one.
Just 32 per cent of voters said they wanted to prioritise cutting spending and debt versus 60 per cent who wanted more investment in public services.
That choice is likely to be at the heart of the next election campaign, and it's one with huge implications.
As we come out of the pandemic years and look to rebuild, the choices we make in the next few years are going to be decisive.
The question will be are we better off making big investments now to get on top of the issues that have built up over years in health, housing, education and infrastructure or, having racked up some big bills to get us through Covid, do we need to cut back on government spending and focus on reducing debt?
According to the polling, voters prefer the first answer. That's tricky for a party like National selling a more austere agenda.
So, knowing their cuts will be unpopular, National is having to do everything possible not to have to mention them.
When really pushed by journalists, Luxon names things like taking cameras off fishing boats, cancelling the TVNZ-RNZ merger or cutting the Hamilton to Auckland rail service.
The problem is that none of these relatively small cuts come even close to paying for the more than $3 billion per year of new spending that National wants to add with its tax cut plan – let alone actually making a decent dent in existing spending levels.
No, if National is going to pay for its tax cuts and spend less overall, it's going to have to cut much, much deeper.
It's simple maths. You can't say debt is too high and the Government is spending billions of dollars more than it should unless you plan to cut billions of dollars out of the Budget.
There's no other way to make the numbers work.
And if you're looking for cuts of that size, cameras off fishing boats won't do it, scrapping a train service won't do it, it has to be in the big cost centres in the Government books – health, housing, education.
Exactly the things voters are saying they want more investment in, not less.
So what's a politician to do?
Well, you can try and put off the day of reckoning as long as possible, as Luxon does when he asks journalists to wait until National releases its full fiscal plan.
Except there's no reason to believe the rules of basic arithmetic will be any different closer to the election.
If you want to spend less money, you have to decide which money not to spend. That's not going to change by the time National sits down to do their fiscals.
So with that option closed, National appears to have no choice except to try and keep ducking the question.
This means this odd and evasive little dance is only going to continue.
Hayden Munro was the campaign manager for Labour's successful 2020 election win. He now works in corporate PR for Wellington-based firm Capital Communications and Government Relations.