Those maddening Nationals, who won’t stay in their place! Deputy Prime Minister Michael McCormack had no sooner debuted as acting prime minister than he dubbed the Treasurer “Scott ‘Santa Claus’ Morrison”, who would be “announcing some goodies” in “an infrastructure budget”.

McCormack made his comments to the Daily Telegraph which, to no one’s surprise, illustrated Tuesday’s story with the Treasurer garbed as a large Father Christmas.

An angry Morrison tried to rein in expectations. “I’m not Santa Claus and I’m not bringing a bag of gifts in May and there won’t be any Christmas in May – what there will be is a responsible Budget,” he declared.

McCormack, Morrison said, “was enthusiastic about the important investments that have been made in infrastructure but I’m sure he would agree with me that our budget will be one that lives within its means”.

Apparently for weeks Morrison has been sending out the message to ministers that the pre-budget line was “responsibility”. And sources who have dealt with the Treasurer in previous years will tell you he’s very hostile to any interference in “his” budget – certainly, one presumes, from a minister who has only just arrived in the cabinet.

In fact we can expect the May 8 budget to be one of “goodies”, probably in various areas, but particularly in income tax, where cuts have been flagged and are a political necessity. Unless there is some rearrangement, this is the last budget before the election.

But from Morrison’s point of view, McCormack’s imagery was totally out of whack with his desired framing. Even within the Nationals there is some criticism of the leader for being inept.

McCormack’s “goodies” appear to be infrastructure projects, although just how much will be new is another matter. In budgets these days it’s often hard to quickly discern the infrastructure announcements from the re-announcements.

The Nationals will always be talking up the infrastructure book, but McCormack – who is Infrastructure Minister - especially needs to do so.

Having inherited Barnaby Joyce’s job, the new leader wants to show he has the same grunt as his predecessor when it comes to delivering for the regions.

When he was pitching for the leadership, one concern was whether he would maintain the Nationals’ profile and muscle within the Coalition. Via a story just before the ballot that said he “will not be afraid to stand up to Prime Minister Malcolm Turnbull”, McCormack signalled to colleagues he’d be determined to hold his own against the Liberals.

Infrastructure is not just centre stage for the Nationals – it is part of the government’s general pitch, as Turnbull goes around the country announcing funding for projects.

It is also integral to the hot debate that is currently running on immigration.

Morrison’s intended topic for his media appearances on Tuesday was a report, “Shaping a Nation”, on the impact of migration. It had been commissioned by the secretaries of Treasury and the former immigration department (now Home Affairs), done in-house, and finished months ago.

The report strongly backs the economic and other benefits of immigration. It also make the obvious point that “high rates of population growth can heighten existing pressures on infrastructure, housing, and the environment”, but sees this as a matter of managing the challenges rather than a deterrent to migration.

There is a certain irony in the two departments’ joint parentage of this report. Treasury is unabashedly pro-migration. But Peter Dutton, the Minister for Home Affairs, always seems to be looking for ways to curb it. Within the Liberals, immigration has become an ideological marker, with Dutton’s own inclination towards lower numbers being in tune with the sentiments of Tony Abbott and conservative commentators.

It was Morrison’s office that (selectively) handed the report out late Monday, and late Tuesday the report was up on the Treasury website but not the Home Affairs one.

The hard line Dutton is the darling of the conservatives, which must rile Morrison, who would also be looking to that constituency for future support. The conservatives see Dutton as reliably one of them; some of them would see Morrison as a soldier of fortune.

If McCormack is trying to make his mark in the early days of his leadership, the ambitious Morrison is under pressure too. In the perennial leadership speculation, he is finding himself mentioned less frequently (although he shouldn’t be written off in the longer term).

Most immediately, Morrison is only too well aware of how crucial this budget is for the government and for him. Governments have given up expecting “bounces” from budgets, but if this one is badly received that will be a disaster for both Turnbull and his treasurer.

As for McCormack - under fire from conservative commentators for alleged fiscal irresponsibility - he will be acting PM, and therefore in the media spotlight, until the end of next week. He appears at the National Press Club on Thursday.

He has put himself in an awkward place by misstepping. The Prime Minister’s Office and the Treasurer’s Office may use the opportunity to try to bring him to heel more generally. They’d judge him as potentially easier to handle than Joyce was. If he submits, his position as Deputy Prime Minister is weakened. If he doesn’t, he could find himself somewhat isolated among his senior colleagues.

Asked on Tuesday whether his Santa comments had tarnished his first day as acting PM, his response was: “Absolutely not, and look, I’ve already spoken to Scott Morrison, and certainly, he’s looking forward to the Budget too.” It wasn’t clear whether that was rather awkward wording or a touch of chutzpah.

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.