It only took 122 years of federal parliamentary sittings ... literally to the day.

Even as journalists surrendered all communications devices in the annual pre-budget lock-up, Parliament convened for the budget session (sans Treasurer) with the swearing in of its newest and perhaps unlikeliest MP, Mary Doyle.

Last month the effervescent Doyle defied more than a 100 years of electoral history to wrest suburban Aston from a shell-shocked Liberal Party.

It was something of an earthquake. A government actually increasing its majority between elections? Unthinkable ... until it happened.

A Labor government delivering the first budget surplus in 15 years, the bulk of these under the Coalition? Tell 'em they're dreaming. Now that's happened too.

In fact, the fiscal improvement in the bottom line set out in this Budget is, according to Treasurer Jim Chalmers, "the biggest ever improvement in a budget in dollar terms".

Luck's a fortune. Or as a pro-golfer once said - was it Garry Player? - "the harder I work, the luckier I get".

Finance Minister Katy Gallagher confided it had been a great deal of hard work, describing it as "actually hundreds or even thousands of individual decisions".

Many of them concerned with finding money for ongoing programs like the Australian Radioactive Waste Agency which was only temporarily funded by the last government. Luckily, radioactive waste just goes away, right?

The opposition's responses are predictable and for the most part unconvincing. Angus Taylor says a drover's dog could deliver a surplus. Jane Hume says the $14.6 billion in cost of living relief including a $3 billion scheme to reduce household energy bills for low income earners, is just a band aid measure when the real villain is inflation.

Does this mean the Coalition will stand in the way of assistance for single parents, JobSeeker recipients, renters and the like? It would be a bold call.

Chalmers has a blunt response to Taylor's claim that anybody could deliver a surplus - "anybody but the Coalition". Fair point.

Suddenly, the political logic of last October's unusually timed budget becomes clear.

Back then, Chalmers banked 92 per cent of unexpected revenue upgrades. It was that discipline which set the stage for 2022-23. Not only did it help considerably seven months later in balancing the books, but it ensured that Labor notched up its surplus in its second budget, not its first. That fact makes it harder for the Coalition to claim the surplus is simply the product of Coalition decisions already dialled in.

Besides, the Coalition's last budget was less an exercise in fiscal repair and more a spend-a-thon as the roar of an approaching electoral waterfall grew louder in its ears. Taylor's right in one key sense though. An embarrassment of riches flowing into the government's coffers from high iron ore, coal and gas export prices, and record income tax flows mean a surplus - as a one-off in 2022-23 - would be hard to avoid.

That's another key Coalition attack line, depicting this $4.2 billion surplus as a fleeting thing to be replaced by big deficits in the out-years.

Yet that is misleading. Australia's economy is fundamentally strong, its deficits low, its debt-to-GDP ratio's significantly better than comparable economies.

In fact even these deficits may themselves not eventuate, or at least not eventuate in their projected scale.

Treasury assumptions necessarily rely on more pessimistic international prices for variables like iron-ore which have done so much to inflate the bottom line this time.

That is prudent. But it is not beyond imagining that these high prices could continue.

Nonetheless, projected deficits for the out years are quite high by Australian standards.

Here lay the political risks for Labor. The budget forecasts lower economic growth for the out years as the effects of repeated interest rate rises cause hardship in the suburbs and a commensurate drop off in consumption.

The Reserve Bank projects the unemployment rate to rise - optimistically - by around one percentage point by the end of next year. And, it could be worse.

So when high interest rates deprive households of spending power to consume for necessities, when businesses start laying off staff because of that low demand and the cost of interest repayments, and when the deficits come in at a cumulative $109 billion over the next five years, then the conditions do not support re-election.

So while right now might be a good time to be in government, according to one credible trajectory - notably the version set out in the budget papers and in gloomy RBA forecasts - it might also turn out to be a short time.

In conditions like that, even a drover's dog would have a chance of unseating a government.