He takes the view that no calls on preferred coalition partners should be made before an election. Parties should simply put their policies to the voters, leaving them to make their choice. There is strong logic to this, and it may have persuaded Mr Peters to make some strong comments about the Greens' proposal. They were, he said, "an attempt by one party to destabilise another party by seeming to offer friendship and collaboration in a deal before the election campaign has even started, knowing full well that the other party has not invited that and does not want that".
Given that statement, a formal coalition between Labour and the Greens would hardly have boosted the prospect of working with Mr Peters after the election. As it is, National may have more reason to cater to him. Unlike Labour, it does not have a party boasting the probable electoral appeal of the Greens ready to enter a coalition agreement. Labour needs nothing else that may persuade Mr Peters he should look elsewhere.
It has been in a formal arrangement once before when it forged a pre-election agreement with Jim Anderton's Alliance for the successful 1999 campaign. There are sharp differences, however, between the situation then, with a National-led government in disarray after the desertion of NZ First, and that of today. Indeed, if anything, that arrangement represents a cautionary tale for the Greens. The Alliance won 10 seats in 1999 but its MPs became divided over how close they should be to Labour. Mr Anderton left to form the Progressive Party, and the Alliance won no seats in 2002.
The 1999 agreement was seen as a means for Labour and the Alliance to present themselves as a credible alternative to National. But it was not necessary and nor did it work out well for the smaller party. Mr Cunliffe has acted correctly in the interests of his own party's prospects and, very likely, those of the Greens.