Chris Penk says he has decided he will not seek re-election as an MP in November, after Prime Minister Christopher Luxon removed his ministerial portfolios earlier on Wednesday."Chris Penk launched a leadership challenge this week, which resulted in today's confidence vote. This makes his role untenable and as such I have removed his portfolios," Luxon said.Paul Goldsmith will pick up the Defence, Veterans, Space, GCSB, and NZSIS portfolios.Simon Watts will become Minister for Building and Construction.The Prime Minister's office has confirmed to RNZ its position is that Penk was challenging for himself, not on behalf of someone else.Earlier on Wednesday afternoon, Luxon held a press conference where he announced he had survived the second attempt to oust him this year.In an abrupt statement to media, he said he had the full confidence of the National Party caucus before leaving without answering questions."Our caucus is united, and it is determined to win this election," he said."Our focus is on National's positive plan to fix the basics and to build the future, so that we realise the incredible potential that sits in this country, and that we set it up for our kids and our grandkids."He was flanked by senior MPs, including Nicola Willis, Mark Mitchell and Chris Bishop.Standing just behind them was Erica Stanford, who was rumoured to be gunning for the top job.Chris Penk at Parliament on Wednesday.RNZ / Zach CornelisenLater on Wednesday evening, Chris Bishop said rumours Penk was doing the numbers for him were "utterly incorrect," and people did not launch leadership challenges on behalf of anybody else."He was not doing the numbers for me. Chris Penk, as the prime minister said, launched a challenge. It didn't succeed, obviously, and any suggestion that he was involved in doing numbers for me is completely wrong.Bishop said there was "no suggestion" Penk was doing the numbers for Stanford either.He said it would be "tough" for Penk, saying he was talented and the two had worked closely together, but he understood why the prime minister had made the decision."He'll be a loss to the government, but that's what happens."Penk, who was ranked 14th on National's list published at the weekend, had earlier denied any involvement in a leadership challenge, after Politik and the New Zealand Herald reported he was doing the numbers for an Erica Stanford bid.Upon arriving in Wellington on Tuesday night, Penk had said he had confidence in Luxon, and would support him in any vote."I've always expressed confidence in the leader. Now is no different."He would not say if anyone had called him about the leadership, saying he would not disclose private conversations, but said reports of his involvement as an instigator were "wrong".He stuck to that position on Wednesday morning, again saying he had confidence in Luxon, and suggested people might be making up stories about him making calls for Stanford."I think everyone else needs to get their story straight because I'm hearing multiple different versions. None of them are true, and as I said, I'm not prepared to disclose private conversations, except only to say I have confidence in Christopher Luxon."Penk had only been promoted to the Cabinet in April, following the retirement of Judith Collins.ACT Party leader David Seymour said for Luxon to remain leader after several challenges showed he was well-positioned to stop the destabilisation in the party.Seymour said he was proud of the way he led his party, saying when it came to working together as a government, ACT had done a good job.RNZ has attempted to contact Penk.