Now that David Shearer no longer has to worry about a knife being plunged into his back - at least not for a while - he needs to tackle another longer-running attempted putsch of a very different but equally serious kind.
Along with other colleagues, the Labour leader is getting increasingly perturbed by the ever more brazen campaign by the Greens to try to displace Labour as the major party on the centre-left.
The worry is not that the Greens might succeed. As last weekend's two television-sponsored polls showed, Labour is still the default option when swing voters tire of National. The worry is that the Greens' behaviour risks working against both parties' wider interests in defeating National in 2014 and securing the keys to the Beehive.
Despite putting in a stellar performance in 2012, the Greens are averaging around 12.5% in all polls - only marginally above the party's showing at last year's election.
In contrast, Labour is now averaging 33%, compared with 27% at the election.
The Greens' objective is to shift those ratios more in their favour. But the reality is that the party is having to put in an awful lot of effort just to stand still.
That is partly why Labour had been relatively relaxed about being pinged by the Greens. Labour's muted reaction, however, seems to have only encouraged the Greens to further test the limits of Labour's patience - the latest example being an incendiary opinion piece in last Monday's Herald written by the Greens' co-leader, Russel Norman.
The previous day's polls threw such articles into sharp relief by indicating that a Labour-Greens governing coalition was now a distinct possibility in the next Parliament. That is not the first time such an outcome has been picked up by pollsters. But it is the first time such a result has been registered by the One News-Colmar Brunton poll or the 3 News-Reid Research survey and thereby conveyed to a mass audience.
Labour was consequently aghast at Dr Norman's subsequent announcement that he was angling for the job of minister of finance in any Labour-Greens coalition formed after the 2014 election.
Labour saw Dr Norman's intervention as poor judgement and a ham-fisted grab for power when the occasion cried out for both parties to show some decorum and highlight the many ways they could work together in the national interest.
Mr Shearer immediately ruled out any prospect of Dr Norman getting the senior finance role, saying that would go David Parker, Labour's finance spokesman.
It is worth noting that Dr Norman did not make installing him ahead of Mr Parker as a bottom line. It is more likely to have been an opening bid for post-election negotiations - one which the Greens could trade off in return for concessions from Labour elsewhere.
But the damage has been done. The thought that the Greens might be given even a junior finance role - as would seem likely - is enough to give many voters the heebie-jeebies.
Such an eventuality requires voters to be slowly acclimatised well in advance of it happening. Handed a political gift, National spent the week revelling in telling all and sundry that Dr Norman had appointed himself to the senior role.
The episode has also left the hugely negative impression that, at the first sign of a turn in the polls in their favour, the two parties were immediately squabbling over the perks of office.
In the Greens' defence, their efforts to push their vote past the 15% level are not just guided by what they can screw out of Labour in coalition-formation deliberations.
They have also watched a succession of other minor parties being destroyed by participating in or propping up governments.
No-one knows how that can be avoided. But one theory is that a more even share of MPs might give the minority partner more control of the major one.
The Greens are also handicapped by only being able to deal with Labour. While still trying to develop further memorandums of understanding with National on areas where they can work together, the Greens reluctantly accepted ahead of last year's election that they could not give formal backing to a National-led government.
The consequent fear that Labour would marginalise them had the Greens warning they were not going to be Labour's ''little brother''. True to their word, their MPs have worked harder and smarter than many in the Labour caucus.
The Greens are assertive. They are decisive. They are media savvy. They take uncompromising, yet often popular positions which Labour, as a major party seeking to attract wider support across the spectrum, cannot match.
Take the Greens' push to ban deep-water oil drilling. Labour says it would allow such drilling as long as there are adequate safeguards - a position designed to satisfy both environmentalists and the commercial world.
But it satisfies neither. The environmental lobby may like the safeguards, but they still do not like the drilling. The commercial lobby likes the drilling, but considers the safeguards to be prohibitively expensive.
Being always forced on to the defensive in this manner has been source of frustration for some Labour MPs, most notably Shane Jones.
He has spoken out against the Greens, most recently criticising them for opposing the development of Northland's resources such as possible oil and gas reserves, which could help cut spiralling Maori unemployment.
The Greens are suspicious that Mr Jones is acting as a mouthpiece for the Labour leadership. While his putdowns are not officially sanctioned by the leadership, neither is he being rebuked for going public with such criticisms.
Mr Jones has upset some in the Labour caucus by infringing on their portfolio responsibilities. But other MPs are quietly applauding him.
Mr Shearer, meanwhile, is understood to have given several senior spokesmen greater rein to criticise the Greens if they seem too out of line with Labour's thinking.
There's concern that Labour did not distance itself clearly from statements Dr Norman made several weeks ago advocating the use of quantitative easing - the de facto printing of money by government.
Essentially, the Greens are the tail that is wagging too much on the end of a rather distracted and sometimes slow-moving dog.
In the end, it is down to Mr Shearer to give the Greens the occasional flick to remind them who is the senior partner in the relationship. But it is a delicate matter. Still, expect a tougher line from Labour from here on.
- John Armstrong is The New Zealand Herald political correspondent.