The run-up to a budget always sees a degree of chaos. But this year it has looked like one of those willy willies that blow up in outback Australia when the wind stirs a storm of dust.

A Middle East war, a fuel crisis, another interest rate rise, calls for extra cost-of-living help amid warnings against high government spending, accusations of prime ministerial lying – they are collectively testing the government’s ability to control how it wants to frame its fifth budget.

But the immediate “narrative” it puts on the budget is one thing – more significant in the longer term is getting its settings right in these extraordinarily volatile times, something we’ll only be able to judge in retrospect.

As is the modern way, some major items have been announced well before Tuesday’s main event, including reform of the National Disability Insurance Scheme and a fuel security plan.

The NDIS overhaul is the big money saver in the budget, a whopping $22 billion. But that is based on heroic, and surely questionable, assumptions, most notably that the scheme’s annual spending growth, now 10%, can be slashed to an average annual 2% in each of the coming four years.

Unless the figures are to be manipulated, this surely defies all previous experience with this scheme. Applying the brakes that sharply looks impossible, especially as some of the details are still to be worked out, and consultations (which often bring concessions) are yet to be held.

If the NDIS’s early cuts can’t be achieved, the government has a hole in its savings package.

It would be interesting to know whether Reserve Bank Governor Michele Bullock is sceptical about the NDIS savings assumption. Bullock,........

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