Scott Morrison will head for the G20 meeting in Argentina on Thursday minus his treasurer Josh Frydenberg and, at this stage, minus a scheduled one-on-one meeting with Donald Trump.

The government switched out Frydenberg, who was due to travel to the summit with Morrison, with the finance minister Mathias Cormann – a nod to the profound challenges of the week, which has included the defection of the former Victorian Liberal Julia Banks to the crossbench.

Morrison’s office also confirmed that there was no confirmed meeting with Trump in Argentina. A spokesman said there was “no pressing bilateral issues at present” so there was “no pressing need for a formal bilateral at this stage”.

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With the government in intensifying difficulty, the former prime minister Malcolm Turnbull also weighed in late on Wednesday, reminding people that conservatives had brought an end to his prime ministership, and blasting News Corp’s editorialising about the events of the week.

Malcolm Turnbull (@TurnbullMalcolm) It was Mark Twain who said “Only fiction has to be credible.” But the @australian satirists outdid Orwell with their editorial today headed “Turnbull moderates blow up a centrist government” A centrist government was blown up; in August and it wasn’t done by moderates.

As well as managing the Banks defection, the government is facing the threat of the referral of the home affairs minister, Peter Dutton, to the high court, and the outspoken backbencher Craig Kelly is continuing to make it clear he could go to the crossbench in the event he is dumped by the Liberal party as the candidate for the Sydney seat of Hughes.

Kelly told Guardian Australia he wanted to “stand up and put my credentials before the preselectors” but in the event he was rolled by moderates in the state, said “I haven’t ruled anything in or out”.

Labor used question time on Wednesday to pillory the Coalition for running “a part time parliament” – a barb which follows the release of the new sitting schedule for 2019 which shows only two sitting weeks are planned before the government hands down a budget on 2 April and goes to the polls for an election in May.

Frydenberg was also asked to explain why he had pulled out of the G20 summit. He replied it was a “leader’s meeting”, which generated mirth in the chamber.

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Morrison rounded on the Labor leader Bill Shorten, declaring him “cocky”. He said the government was rolling out a policy agenda which included cancelling the citizenship of people who engage in terrorist acts – legislation expected to be introduced to parliament this week.

“This is a government that knows how to keep our economy strong, how to keep Australians safe,” Morrison said. “We are getting on with the job of doing all of those things.

“This is a leader of the opposition who thinks all he has to do is to turn up in parliament.”

It remains unclear whether Labor will be able to secure the votes to get Dutton referred to the high court to test if payments to childcare centres owned by his family trust breach the constitution. The government has launched a strong rear-guard action to head off the sortie.

The manager of government business Christopher Pyne on Wednesday threatened to retaliate against independent Kerryn Phelps and two Labor MPs if parliament decides to refer Dutton to the high court to test his eligibility to sit in parliament.

Phelps labelled Pyne’s threat “dirty tactics” and warned she would “not be intimidated” but did not reveal her own position on the referral.