If Jacinda Ardern leads Labour to a second term in Government, the question of who should be Deputy Prime Minister is problematic.
Part of the problem goes back to how she became leader. It is a uniquely Labour problem involving Labour deputy leader Kelvin Davis and the man many people assume is the deputy leader, Finance Minister Grant Robertson.
Deputy Prime Minister is not just a titular role.
When Ardern took time off to have a baby in 2018, or had long trips overseas, Deputy Prime Minister Winston Peters was required to take charge of the Government, run Cabinet, be prepared to answer any questions in Parliament and at press conferences on any Government matter.
The least problematic option but also the least likely option on current polling for New Zealand First would be Peters returning to the job, although it is not impossible.
If the Greens fall below 5 per cent, the New Zealand First Party makes it back, and Labour needs New Zealand First to govern, Peters could easily expect to be back in the job.
That would be no big deal. Peters did a perfectly good job deputising for Ardern when needed. And there was no issue with him having the job as Parliament's most experienced MP.
A coalition between Labour and the Greens could see the Greens seeking the job.
There are several reasons Labour might not want to give it to them.
If, for example, Labour was short by only one or two seats for a majority in the House, there would not be a case for the Greens to have the deputy Prime Minister's job as well.
Under the current two-party Coalition, Labour's 46 MPs was well short of a 61-seat majority and New Zealand First brought nine MPs to the coalition – still short.
The Greens' eight MPs gave the Coalition support on confidence and supply issues.
If Labour won a majority of the seats on Saturday but chose to enter a formal arrangement with the Greens, there would be even less of a case for the Greens to have the deputy role.
The Greens themselves might have second thoughts about seeking a place in full Coalition around the Cabinet table.
It would require a Green Deputy Prime Minister from time to time having to defend actions of poorly performing Labour ministers and departments.
It would require defending issues around free trade deals, the NZ Defence Force and intelligence agencies that it might not necessarily agree with.
If the Greens support was required by Labour but the Greens preferred to remain outside Cabinet, there could be no Green deputy Prime Minister. The Prime Minister and the deputy need to be members of Cabinet.
If the Greens did hold the post of Deputy Prime Minister, it would almost certainly go the James Shaw rather than co-leader Marama Davidson because of his sheer experience.
The one advantage for Labour in having a Green or New Zealand First deputy would be it would avoid the conundrum over Labour deputy leader Kelvin Davis.
To understand Labour's problem, you have to understand how he came to become deputy leader to Jacinda Ardern in the first place.
The Labour Māori caucus was loyal to Andrew Little last term, almost to the end, even when the polls started heading south for Labour two months from the 2017 election.
Ardern as deputy leader was loyal to Little as well and had vowed not to challenge him.
Little was weighing up whether to give up the leadership with the election so close and was initially reluctant to stand aside, and the Māori caucus was reluctant for him to do so.
He had invested three years into getting the party into shape after the failures of David Shearer and David Cunliffe.
The night before Little stood aside for Ardern, it had been put to the Māori caucus that Davis could become deputy leader to Ardern.
That offer, conveyed by another Ardern confident, Chris Hipkins, helped shift the Māori caucus support immediately behind Ardern.
It was not exactly a token appointment because Davis represented an important power bloc within the caucus, but it was not exactly based on merit either. It was political expediency.
The problem is that Davis, while he has his strengths, appears not to enjoy some aspects of the acting Prime Minister's job he has had to undertake as No 3 in the Government – namely the public-facing ones such as standing in for her in Parliament or in media interviews.
He is not good at it. The sorts of tasks he most dislikes would only increase as Deputy Prime Minister.
Many people think Robertson is the deputy because he is Ardern's closest political confidant, and he is seen as the de facto deputy.
They are such strong political partners that they are known as "Gracinda". Oscar Kightley, the MC at Labour rally in Wellington, likened them to salt and pepper and cornflakes and milk.
Robertson, as the senior MP for the region, introduced her onto the stage and was by her side afterwards when a television reporter asked him if he would like to be Deputy Prime Minister.
Ardern stepped in and said no thought was being to portfolios until after the election.
Unlike Davis, Robertson thrives in the public spotlight.
It is usually arranged for Davis to be out of the House on a Thursday when Ardern is also not there, leaving it to Robertson, No 3 in Labour and No 4 in Government, to run the show.
As success goes, there are worse problems to have than a reluctant deputy. But what could be done about it?
No one is going to move against Davis. If Labour formed a majority Government and Davis wanted to be Deputy Prime Minister, he would get it and his office would be bolstered with more support staff.
It is a difficult issue for Davis too. He carries the aspirations of many Māori on his shoulders as Labour's most senior Māori MP and even if he did not want the job, he might well feel obliged to take it, depsite being a sitting target for the Opposition.
It would be very peculiar for Davis to elect to stay as deputy Labour leader and to suggest that Robertson be Deputy PM – although that is not impossible.
It is possible that after the election that Davis could decide to stand aside as deputy and take on greater ministerial responsibilities, clearing the way for Robertson.
Or he could give it a go for say a year and then decide whether it was creating too much anxiety.
It is not problem anyone in Labour would admit to thinking about before the votes are counted on Saturday, or even admit to having. But victory would not come without problems.