The appointment of Christine Rankin as a Families Commissioner is so wrong on so many levels that, unsurprisingly, it took John Key some time to mount a defence. Finally, clutching at one strand, he has made much of Ms Rankin's "very strong" advocacy of the rights of abused children over the past two or three years. Sadly for the Prime Minister, that justification is as misplaced as any other that could be offered.

If Ms Rankin had been appointed Children's Commissioner, it might be appropriate. But this four-times-married woman has been appointed to a body whose brief - providing a voice for New Zealand families - is altogether different.

Fresh questions about Ms Rankin's suitability have been prompted by revelations about her latest marriage, which occurred soon after her husband's previous wife committed suicide. But well before this, it was clear that her appointment was the Government's most glaring error to date.

Much has been made of her supposed ability, but there is little concrete evidence to underpin that. Her time as the head of Work and Income was most notable for the ill-considered spending that prompted well-founded accusations of a culture of extravagance. Nothing that she has done subsequently has warranted a reappraisal of her reputation. While she is forthright and determined, the American saying that a person is "all hat and no cattle" would seem to apply.

Given this, and the fact that her actions damaged a previous National Government, it seems extraordinary the Cabinet could have considered, let alone approved, her appointment to the commission. Increasingly, it smacks of political partisanship. In such a light, it might not be irrelevant that Ms Rankin was filmed dancing with her future husband, Kim MacIntyre, on election night at the National Party's SkyCity celebrations.

Ms Rankin's reaction since her appointment has only intensified questions about her. Her behaviour has incorporated a carefully crafted victim status - "I've really been treated quite appallingly" - a strong dose of arrogance and a refusal to even contemplate criticism. Just when she should have kept her head down, she chose to adopt her most strident self-righteousness on television's Sunday programme. The Government's public relations advisers must have been appalled.

This misjudgment was compounded when she dismissed comments by the Labour Party leader, Phil Goff, by saying, "Oh, what a lefty he is". Does this mean that people who approach her on families matters will get short shrift if they are not of the right political cut? With one unthinking comment, Ms Rankin confirmed her inappropriateness for a neutral public office.

She must have known her history of personal relationships and, in particular, the circumstances of her fourth marriage would be raised if she took a role such as that of a Families Commissioner. Comparisons with the ethos of the commission would automatically be made. She can only have calculated that the rhinoceros-like hide that she customarily adopts when confronted by criticism would enable her to weather the storm. Some members of the Cabinet must also have been aware of the baggage that Ms Rankin would bring to the job. Their judgment was equally fallible.

Mr Key is refusing to walk away from Ms Rankin. He insists that she can "operate properly" as a commissioner. He is wrong. Ms Rankin will be unable to say anything about family issues with any degree of credibility. She will be assailed for every comment that she makes. Her appointment was a mistake from the start. It is now completely untenable.