If there was any doubt Sussan Ley faced an impossible challenge keeping the Coalition together, proof arrived before breakfast on Wednesday.

Ley was yet to even step up to her first question time opposite Anthony Albanese when she was badly undermined by the Nationals MPs Barnaby Joyce and Michael McCormack on the question of net zero carbon emissions by 2050.

The former leadership rivals put down their weapons in an interview with The Australian, declaring they would push for the junior Coalition partner to ditch net zero, locking in a fight with the Liberals on policies ahead of the 2028 federal election.

Both men have been all over the map on the issue.

It was Joyce who signed the Nationals up to Scott Morrison’s policy back in 2021, in exchange for an extra seat in cabinet, and McCormack has previously advocated for the need for net zero plans to limit the damage from climate change.

But, even as the Liberals and the Nationals both start policy reviews on this very question, the pair said net zero was bad for regional communities and had to go.

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McCormack will vote for Joyce’s private member’s bill to reverse Australia’s net zero stance, if it ever comes up for a vote in federal parliament. He insisted Wednesday’s declaration was not about weakening David Littleproud as Nationals leader, despite conceding to Sky News he still has a bit of political fight left in him.

“We’re not gelded, we’re not emasculated,” he said. “We’re very much virile and out there.”

For Joyce, animated as he explained developments to the Canberra press gallery, none of this is new at all. He has called net zero “treacherous” to Australia’s security, hit out at the “lunatic crusade” to cut carbon emissions.

“People feel that the process has been obfuscated, people are furious,” he said.

“You get to understand the sort of fury that [they have] in regional areas. We have in meetings people crying, we have in meetings people feeling bullied. They believe the government is just running roughshod over them.”

Sussan Ley fought to bring the Nationals back to the Coalition and promised all policies would be carefully reconsidered. Photograph: Lukas Coch/AAP

The Nationals senators Matt Canavan and Ross Cadell are leading the party’s review of net zero, commissioning new economic modelling and preparing for a series of debates with colleagues. One Nationals insider told Guardian Australia this week a vote on ditching net zero would likely have two to one support.

That’s all downside for Ley.

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After the thumping the Coalition received on 3 May, Ley fought to bring the Nationals back to the Coalition and promised all policies would be carefully reconsidered.

Opposition from the Nationals is likely to crash head-on with calls by moderate Liberals for the Coalition to stick with net zero, part of efforts to win back metropolitan voters concerned about the warming climate.

Privately, some Liberals say Joyce is hurting their chances again, despite Labor being comfortably in power for at least six years, when the renewables transition will be significantly further advanced.

That means the latest push just reinforces with voters why they rejected the Coalition earlier this year, undermining Ley’s position even more.

Liberal elders Nick Minchin and Pru Goward had front row seats for the drama at Parliament House on Wednesday. Ley’s handpicked chairs for the postmortem election review, their recommendations will feed into the impossible choice facing the Coalition in the months to come.

It’s all upside for Labor. The climate change and energy minister, Chris Bowen, couldn’t conceal his delight.

“Even Peter Dutton backed net zero,” he said in question time. “While the world moves forward on climate action, the Coalition still wants to take the country backwards.”

Tom McIlroy is Guardian Australia’s chief political correspondent