Malcolm Turnbull’s Liberal deputy has rejected suggestions the prime minister should consider stepping down by Christmas if the polls are still bad.

Julie Bishop was responding to an extraordinary challenge by former deputy prime minister and Nationals leader Barnaby Joyce.

Mr Turnbull’s leadership is under a cloud after the coalition government lost 30 Newspolls in a row, the same as one of the metrics he used to topple Tony Abbott in 2015.

After the poll was published on Monday, Treasurer Scott Morrison, Home Affairs Minister Peter Dutton and Energy Minister Josh Frydenberg all openly said they would be keen on the top job in future.

Then Mr Joyce – who was recently forced out of the Nationals’ leadership after a public stoush with the prime minister over the fallout from his affair with a staffer – went on Sky News.

“Towards the end (of the year) near Christmas you’d have to start asking those around you what do they believe is the proper course of action from that point forward,” Mr Joyce said.

But the foreign minister said all the talk was hypothetical.

“I don’t agree with Barnaby Joyce. The prime minister will lead us to the next election,” Ms Bishop told ABC radio on Tuesday.

As for her ministerial colleagues, Ms Bishop said they were “presumably … speaking about their future ambitions”.

They’ve all said that Malcolm Turnbull will lead us to the next election so I think we need to look at their comments in that context.”

Ms Bishop ducked questions about whether she too aspired to be prime minister one day, saying her priority was to focus on the jobs and responsibilities she held now.

Nationals deputy leader Bridget McKenzie also disagreed with her colleague Mr Joyce, insisting the Turnbull government is delivering.

“I understand that some people want to comment on the Newspoll and what it may mean for Malcolm Turnbull but I think we need to focus on is what the Newspoll is telling us about Bill Shorten,” she told ABC radio.

Senator McKenzie cited Mr Shorten’s Newspoll results in Queensland following what she described as his “shifty approach” to regional mining jobs, especially during the Melbourne Batman by-election.