Former Liberal opposition leader John Hewson says the Coalition's $158 billion tax cut plan will be unaffordable as the Australian economy weakens.
He also described Prime Minister Scott Morrison as an ad man with a "pocketful of slogans" but little detail, who needed to "establish credibility" as a leader through serious reform.
Dr Hewson was speaking at the Sir Roland Wilson Foundation's post-election policy forum on Tuesday titled "Miracles or Mayhem?".
Reflecting on the forum's title, the Australian National University Crawford School of Public Policy professor said the Morrison government "could go either way".
While the prime minister was in a "much stronger legislative position than he hoped to be", Mr Morrison did not have "any particular personal policy agenda", Dr Hewson said.
"He is an advertising guy, he does have a pocketful of slogans, if you ask him a question he gives you a slogan, don't ask him a second question or for detail, he hasn't got any," he said.
"The slogan was 'we have a strong economy and I'll make it stronger' which defies logic because the economy isn't strong and the numbers since the election have revealed it isn't as strong as they'd like us to believe and in fact the biggest risk in terms of the future of the government is whether or not our economic circumstances unravel further."
Dr Hewson said the risk of a recession had increased significantly, with global growth slowing, financial markets volatile and Donald Trump's trade war hanging over it all.
Coupled with lower consumer spending, record levels of household debt, falling house prices, flat wages and rising cost of living, there were "significant constraints on moving the economy forward", he said.
"The tax cuts that have been promised of course would offer some sort of short term relief but I personally doubt that they are affordable as you move into the 2020s."
The weakened position meant it would be difficult to deliver on the hundreds of millions of dollars in election commitments and the succession of budget surpluses promised,Dr Hewson said.
It also meant the government would likely try to "pull back" the impact of the tax cuts.
However Dr Hewson said Mr Morrison had a "unique opportunity" to pick a few issues to make serious progress on.
"There are issues there that are of medium to long term structural significance which I think should be picked up by ScoMo if he wants to establish credibility as a leader which would carry beyond this election," he said.
Climate change, addressing disadvantage and creating a China policy should be key priorities, he said.
"From a personal point of view , from one who did lose an election by trying to win that point about substantive reform, ironically the need for reform is the greatest when it's politically the most difficult to do and that's the case right now," Dr Hewson said.
"You can go across just about any area of public policy and say there's a substantial case for broad-based, medium to longer term reform which is hard to talk about in the short term political cycle which is dominated by daily point scoring and blame shifting."