With Luxon's leadership under pressure, who could be lined up to take the top job?

As Christopher Luxon's leadership comes under fresh pressure with rumblings of a rolling, who else could be lined up to take the top job?It was unclear whether he'll call another confidence vote in himself, just four months after the last one when word of a potential coup hit the media.There's no obvious single challenger within the caucus, but a few names stand out.Nicola WillisNicola Willis. (File photo)RNZ / Louis DunhamFinance Minister and National deputy Nicola Willis has a big profile as Finance Minister, and was a savvy political operator, strong communicator and formidable debater.Willis had navigated her way through the fuel crisis well, explaining the situation and communicating effectively.She might have been considered a frontrunner a couple of years ago, but her stock and standing had become increasingly tied to Luxon over the term.As such, she had been tarred with the same brush.Willis living in Wellington could count against her, with some insiders suggesting the party's leader should be based in the electorally important Auckland.However, she could easily be paired with an Auckland-based deputy.Chris BishopChris Bishop. (File photo)SAMUEL RILLSTONE / RNZChris Bishop was the name on everybody's lips late last year during a burst of chatter about a potential coup which ultimately amounted to nothing.He's a safe pair of hands, effective media performer and gets through a tonne of work, trusted with a suite of weighty portfolios including Housing and Transport.Bishop was deeply ambitious and understood the game of politics better than most.Equally, that animal instinct had seen him burn relationships with the caucus, with many still recalling his role in Todd Muller's ill-fated and brief rise to the top.Bishop did have a proven record in flipping a red seat blue - with his Hutt South electorate. But like Willis, his location may be seen as a downside.Erica StanfordErica Stanford. (File photo)RNZ / Samuel RillstoneErica Stanford was widely considered a potential leadership contender.Stanford had proven herself in tricky portfolios this term, impressing as Education and Immigration minister, which had also given her decent name recognition.However, she was not as tested as Willis or Bishop and it's unclear how she would perform on finance and the economy, given her lack of experience in that area. Some in the coalition had doubts over whether her successes would extend outside of her portfolios areas.Stanford was an Auckland mum, relatively young, and sat on the progressive left of the caucus, which could be considered an asset in attracting female centrist voters.Other possibilitiesSenior MPs Simeon Brown - the party's campaign chair - and Mark Mitchell have also been floated, but they're more likely deputies than leaders.Putting either of them in top positions could keep the conservatives of the caucus happy, given Willis, Bishop and Stanford were liberals.National's caucus meets at Parliament at 9.30am on Wednesday.