Malcolm Turnbull's darkest political days were very illuminating of the man.

This was after he had been bumped by Tony Abbott from the Liberal leadership and when he was still dumbfounded at being sideswiped from his destiny.

"They complain," he'd say, referring to fellow Liberals, "that I'm popular with Labor voters. I thought that was the whole point; that you take supporters from them."

This is the Malcolm Turnbull that has befuddled and disappointed Australians since coming to the prime ministership.

They simply got him wrong. He is not a shape-shifter in the way Kevin Rudd was, but he has nevertheless confounded classification.

Why? Because he is a firm occupant of the Australian centre. He is not from the left. And he is not from the right. He is a political bowerbird who steals anything that could look blue.

This is the man who was both encouraged by then Labor prime minister Paul Keating to join the ALP's federal parliamentary ranks, and later implored by former Liberal prime minister John Howard to stay in politics in case Mr Abbott proved to be a flop.

How better to explain the Turnbull enigma? Mr Howard's private Plan B for the Liberal leadership was also once Mr Keating's target for high-profile recruitment.

This is the man whose conservative government could produce such an extraordinary federal budget that pilfered so merrily from the Labor cupboard, with nary a concern about trampling on precious Liberal taxation shibboleths.

In the name of ruthless pragmatism, he and Treasurer Scott Morrison have launched an extraordinary $6.2 billion raid on the big banks and an $8 billion plunder from taxpayers in the form of a 0.5 percentage point increase to the Medicare Levy to fully fund the National Disability Insurance Scheme (NDIS).

Mr Turnbull has not only firmly embraced the NDIS, a Labor legacy, but used it to batter the Labor Party for insufficiently provisioning it.

And the Treasurer, with an unconventional post-budget speech on Wednesday, used the story of his brother-in-law Gary Warren's battle with multiple sclerosis, to skilfully and passionately remodel the full-funding of the NDIS into a Liberal cause.

Budget attempted to poison fertile ground for Labor

Coming a week after the Coalition's sudden embrace of needs-based schools funding and the brazen redeployment of Julia Gillard's schools tsar David Gonski, the entire Government was acting in the fashion of its bowerbird Prime Minister.

It was a big-spending, big-taxing budget that was not Labor-lite, but busy in its centrist repurposing of education and health policy.

That said, Health Minister Greg Hunt's creation of a Medicare Guarantee Fund — supposedly a special account covering every Australian's Medicare costs — was the final surrender to Bill Shorten's effective campaign.

No government before has considered it necessary to hypothecate revenue into such a fund. Its alternative name could be the Mediscare Insurance Scheme.

"A political budget for the times," was how one Liberal MP sardonically put it, as if holding his nose at some the document's antithetical ingredients.

It certainly wasn't a budget the Abbott Government could have delivered. And judging by Mr Howard's comments in Perth this week, his unease with the budget was not restricted to the tax strike on the big banks.

But it's a budget that might work for Mr Turnbull if it engenders a sense of purpose his government has been lacking.

The budget attempted to poison once fertile ground for the Labor Party.

Notably, Mr Shorten's budget reply speech made no mention of Gonski by name, demanding only that the Government reinstate $22 billion in schools funding.

Labor's claim that it fully funded the NDIS — a claim the Opposition leader repeated on Thursday night — was undercut by Mr Shorten's decision to support the increase in the Medicare levy, albeit restricting it to those earning more than $87,000.

But Mr Shorten has proven much more adept than Mr Turnbull at recasting the political battle, whether that be about values, fairness or social equity.

Mr Shorten's speech employed plenty of class war rhetoric, about millionaires and the big end of town, versus the battlers and the middle class.

The PM would be unwise to underestimate the Labor leader's ability to reframe the Medicare levy increase into a fairness question.