Both Labour and National start the election year with partner problems.
National's problem is that we don't know who their partners are - or whether they will have any. There's quite a list of possibles: the Maori Party, United, Act, the Conservative Party, New Zealand First. But they are only possibles.
The ones signed up with National may not make it to Parliament and those who do may not run with National.
National could very easily trounce Labour in the polls but lack the numbers to form a government. The out-polled Labour Party may well form a government because it does have a support party.
Labour's partner problem is the opposite of National's: voters know only too well their potential partner. The Greens consistently poll more than one vote for every three that Labour pulls. That means by the logic of democracy the Greens making up a quarter of any Labour-led government with ministers, parliamentary roles, policy and decision-making.
The problem that the Greens present for Labour is that they are more red than green. They have chewed off a great chunk of votes from Labour's left flank while scaring centre voters away from Labour to National. The Greens squeeze both ends of what was Labour's voter base.
National's problem is that none of its sure partners is successful enough. Labour's problem is that its sure support partner is too successful.
The Greens' very success runs the risk of denying them the possibility of government. A vote for Labour is a vote to put the Greens in power.
The Greens provide National with an easy strategy this election. National can wheel out the mad, bad Green Party policy and declare it the would-be Labour-led government's.
That serves to scare even more voters National's way and put Labour on the back foot.
Labour can't ignore the claim. The Greens are polling too high for that. Accepting the policy makes Labour look weak which, in turn, drives more votes National's way. Rejecting the policy upsets Labour's left-wing membership and activist base, drives more left votes to the Greens and risks a bun fight with the Greens.
It would seem logical for the Greens and Labour to sit down ahead of the election to establish policy agreements and disagreements and a broad-brush approach to ministerial positions. But politics isn't logical.
The Green membership would conclude their MPs were sellouts, giving away the bulk of their policy before the election and Labour would risk losing more centre voters.
Centre-right voters are smart. They know to vote tactically to ensure National has the numbers.