National party leader Todd Muller has resigned, saying the job has become untenable from a health perspective.
New Zealand Herald political editor Audrey Young told Kerre McIvor she believes Todd Muller has had a mental breakdown.
"I think he's largely pointed towards that himself. It has all become too much for him, and last week was just the breaking point."
Young says the pressure of the job would've got a lot worse and more intense towards the end of the campaign, with every word subject to scrutiny.
"It's all unfortunate, I feel very sorry for him. You can't know how you are going to deal with that level of pressure until you are in that job."
Young says the two or three contenders for the leadership, include Judith Collins, who could be an emergency option.