Maurice Williamson's resignation as a minister was forced by "a significant error of judgment" in the words of Prime Minister John Key.
As soon as Key discovered that Williamson had called the police about their investigation into domestic violence allegations against businessman Donghua Liu, Key had no option.
It was clearly not a close call, but a clear breach of acceptable behavior.
The fact that Williamson said he was not trying to interfere in the police process - and even made that clear to the police - is no mitigation.
The call was made and that, of itself, constitutes interference, whether intended or not.