In what may be the most amateurish coup attempt ever, Chris Carter has killed his own career in a way that ensures none of his colleagues could ever back him. Unintentionally, he's made Phil Goff's leadership more secure and given him a fresh opportunity

In law enforcement circles they call it 'suicide by cop'; those situations when someone acts in an aggressive, confrontational way, thereby provoking police into a lethal response. That's exactly what Chris Carter has done to his career today by sending a letter attacking Phil Goff's leadership of the Labour party to three members of the press gallery.

With the news so fresh, I'm writing this with imperfect knowledge. But it seems that Carter has chosen to go out in a hail of bullets like some kind of Butch Cassidy, rather than the dignified exit offered him by Goff just weeks ago, when the Labour leader opted not to sack him for his, shall we say, relaxed use of his ministerial expense account. It's classic self-destruction, and despite his claim that union-based MPs were set to try to roll Goff next week, union sources tell me that no such plot existed.

It's hard to imagine why the unions would suddenly rear up in opposition to Goff, anyway. Their own Andrew Little presides over the party and has just declared his intention to stand in the New Plymouth seat next year. They are igniting the biggest campaign in years against National.

If any kind of coup was being conceived, the timing midway through the election cycle is hardly very appealing. The only argument that could have been made in favour of acting now is that in the past few weeks Goff has actually started to look the part.

National has had the wobbles of late. In many ways, my post last week came too soon. Following National's consumption of the political dead rat that was mining on Schedule 4 land and its rejuvenation of the union movement by proposing aggressive but rather piddling changes to labour law, it's followed up this week by:

• deciding not to change blood alcohol levels that Steven Joyce only months ago called "ridiculous"
• floating the idea of doing away with that middle-class vote winner, interest-frees student loans
• getting in a tangle over overseas investment rules as it tries to fence in Winston Peters by being anti-investment on one hand, while working through a review aimed at encouraing more overseas investment, on the other.
• trying to argue black is white by saying that the gaps between incomes in Australia and New Zealand haven't widened.

Key has been looking both indecisive and more like a politician, neither of which does him any good.

And then this. Labour shoots itself in the foot, National gets time to re-group. Labour looks even less like a goverment in waiting, more like a party in limbo.

Carter, while claiming to have done this for the good of the party and to give momentum to colleagues pondering a leadership challenge, has ensured he has no friends left and no party support.

It's a pitiful end for New Zealand's first openly gay MP – and be in no doubt, this is the end. He wouldn't win a by-election and he will be expelled from the party.

What's striking is just how amateur an end it is – a letter addressed in his own handwriting, an initial denial when confronted by Goff, a protest act of such blatant and graceless disloyalty and pique that no-one can possibly rally behind him or his cause. However sincere Carter may be in his opposition to Goff, it looks like petulant retaliation over his demotion for expenses. Carter has no chance of winning that argument.

As I say, death by cop.

The letter and the 'plot' behind it has all the subtle skill of a boarding school prank.

The only thing you can say in his favour is that at least he did his own dirty work and expressed genuinely held beliefs.

If David Cunliffe did have any plans of a bid in the next 18 months he will be furious tonight. Carter's actions have forced him to publicly rule that out. On the other hand, he will be quietly pleased that the letter and subsequent media coverage establishes him more firmly as the heir apparent, at the expense of perhaps Maryann Street and Trevor Mallard.

And what about Goff? Carter's denouncement of his leadership and his inability to win next year hurts, but only so much. Everyone knows the mountain he has to climb and Carter's outburst doesn't change that.

The fact for Goff to focus on tonight is that with crisis comes opportunity. Indeed, the next few days are critical for him. He would rather be comparing pay rates with Australia, but he now has the chance to show a steely side, even a little passion. What's more, it removes a troublesome MP and gives him the safe Labour seat of Te Atatu to hand out to some fresh – and loyal – new talent.

Perversely for Carter, this has given Goff some of his best television moments since he's been leader, allowing him to look decisive and to take the high moral ground on expenses. Carter, on the other hand, looks finished.