Prime Minister Malcolm Turnbull and Treasurer Scott Morrison will be relying heavily on the old dictum ‘a week is a long time in politics’ to sell the budget.

Because they themselves have heavily discounted practically everything they have said on key issues that have given context to this year’s fiscal fix.

Mr Turnbull will be hoping voters can’t recall the 263 times Labor has collated when government ministers opposed a banking royal commission over the past two years.

It was unnecessary, a Bill Shorten stunt and, besides, “we have already acted”, he said.

Mr Morrison assured the nation that the corporate regulator ASIC was “a tough cop on the beat”. So tough not one banking executive ever lost his or her job despite the media exposing appalling behaviour.

It made very hollow Mr Turnbull’s response to the news that AMP’s chairman Catherine Brenner resigned after a board crisis meeting gave her and in-house chief counsel Brain Salter their marching orders. This was after the royal commission raised the prospect of criminal charges.

The Prime Minister tried to tie those developments to “very substantial reforms in terms of protecting customers” that he had put in place over “the past two years”. These are the reforms that the tough cop either couldn’t or wouldn’t apply.

By their own admission, the government’s top economic ministers missed the boat on the banking scandals because they lacked foresight or insight into the quagmire. They get it now with “hindsight”.

Mr Shorten is unforgiving and he is sure voters are not impressed with the same blindsided ministers now wanting to give the banks $17 billion worth of tax relief. That’s the revised cost of their share of the corporate tax cuts that are the centrepiece of the government’s enterprise tax plan.

The Opposition Leader has hardened his attacks, bolstered by reactions he has been getting around the country.

“It’s bad enough the Prime Minister can’t say sorry for standing in the way of the royal commission, denying people’s hurt and delaying their justice. Now he wants to compensate the perpetrators,” Mr Shorten has said.

There is some speculation that the Treasurer could try to modify the plan in some way. But it will be hard for him to do that with any credibility. It is surely too big an ask coming on top of the ditching of the Medicare income tax levy rise to fund the National Disability Insurance scheme.

Having claimed for one year that the levy rise was, according to Mr Turnbull, “a vital exercise in fairness”, and, Mr Morrison said, one they would take to an election if the Senate continued to block it.

“We stand by this policy absolutely,” Mr Morrison insisted.

The Treasurer accused Labor of “playing politics with it” and claimed it had left the scheme unfunded – despite Labor’s then-treasurer Wayne Swan raising the Medicare levy by half a percentage point to do just that.

That has raised more than $20 billion between 2014-15 and 2018-19. Mr Swan now says because the NDIS is being phased in his hypothecation has unspent money in the bank, as it were. He allocated $14.3 billion over seven years to roll out the scheme.

Mr Morrison now says the dramatically improving economy has replaced the need to raise the levy. Indeed, as the Deloitte Access Economics Budget Monitor says, “the rivers of gold are running again … doing the budget plenty of favours”.

The biggest is company tax revenues are up 23.3 per cent on the previous year.

Deloitte’s chief economist Chris Richardson is warning the good times won’t last and cautions against a pre-election cash splash. Mr Morrison himself is hedging on his commitment to budget surpluses of at least 1 per cent of GDP in the medium term, that is four to eight years away.

But the fact is it’s not the medium-term he is worried about. It is very much the near-term. Getting voters to believe him and the Prime Minister is his immediate challenge.

Paul Bongiorno AM is a veteran of the Canberra Press Gallery, with 40 years’ experience covering Australian politics.