Long-time National MP Judith Collins emerged victorious in tonight's leadership vote and is determined to win back the treasury benches come September 19.
And she has set her sights on Prime Minister Jacinda Ardern.
"There is no chance at all that I'm going to let Prime Minister Jacinda Ardern get away with any nonsense when it comes to the economy and doing her job. We will hold her to account."
She said the Prime Minister had only three ministers that she had confidence in – whereas she had a whole team.
"I am hoping that the National Party will collectively crush the other lot, come September 19," she said, when asked if she could shake the nickname 'Crusher'.
Asked about her first job as National leader, Collins replied: "Winning".
"My focus as leader will be helping rebuild our communities and dealing with the economic and jobs crisis by getting Kiwis back to work," she said.
"Only National has the experience and skills to get us through this. We are a strong team and I look forward to forming the next Government."
New Zealand's economic recovery and what she suggested was an incompetent Government was a theme of Collins' late-night press conference.
"We're just going to have the most fun as we take back the country."
But she did concede it would be hard work – there are just 66 days until the election and the campaign period is only weeks away,
Collins warned that Ardern should not be underestimated.
Asked what she had over Ardern, she said: "Experience, toughness and the ability to make tough decisions."
Collins would not talk about who else ran for the leadership, or the deputy leadership.
Tonight was her third crack at National's leadership.
She put her hand up to replace John Key after he resigned as Prime Minister in 2016.
After it became obvious that Bill English – who was Key's preferred choice – had the numbers, she withdrew herself from consideration.
When Bill English resigned as National leader in early 2018, she – along with fellow National MPs Mark Mitchell, Simon Bridges, Amy Adams and Steven Joyce – ran for the top job.
"It's third time lucky," she said, when asked about the leadership run.
She confirmed there would be a minor re-shuffle in the next few days or weeks.
But finance spokesman Paul Goldsmith would keep his portfolio.
nzh-inline-image id="40822729" position="left" />
When asked about Michael Woodhouse keeping his health portfolio, Collins said there were "still a few things to work out".
She also confirmed that none of the MPs who had previously announced they were resigning from politics, such as Paula Bennett, have indicated they would be coming back.
Earlier tonight, MediaWorks reported former leader Simon Bridges was not entering the leadership race, and that Mitchell and Louise Upston have formed a team to bid for the top jobs.
MP Melissa Lee said the caucus would select its new leader tonight, RNZ reported.
At 8.30pm, clapping was heard from the caucus room.
Louise Upston told media after landing in Wellington that Muller's resignation had come as a "total shock".
"It's a real shock - there's no two ways about it. My thoughts are with him and his family and as the National Party caucus we've got a job to do to fill that gap."
Upston said she didn't think caucus would be "rushing" their decision.
"It's really important for the country to know the National Party has their best interests at heart and so we will be selecting a leader that we believe has the attributes and ability to lead our fantastic party for now and in the future."
Long-time MP Gerry Brownlee might also be an option for the deputy role, as is finance spokesman – and Bridges backer – Paul Goldsmith.
Current deputy, Nikki Kaye, is likely to be chairing tonight's meeting.
She would not be drawn on whether she would put herself forward for leader, or deputy leader, or who she'd support.
There is no script as to how tonight's meeting will run, but there is every chance a new leader will emerge tonight.
Speaking to reporters on the way into Parliament this morning, Mitchell said tonight's caucus meeting was about deciding on a process to follow.
Almost all MPs door-stopped by media at an airport, or in front of Parliament, today sent Muller and his family their sympathy and best wishes.
"The important thing is we have compassion for Todd at this time while we work through what has been a very difficult time," Kaye said this afternoon.
Speaking to reporters in Wellington airport, Paula Bennett – who announced earlier this month that she would not be contesting the election – would only say the caucus has a "big decision to make".
She said she had "no comment to make about anything", when repeatedly questioned on today's developments and what will happen tonight.
But she did say: "These are just difficult times for the party and the caucus – so we are just going to work our way through that respectfully."