Nick Smith should have offered to resign yesterday. The Prime Minister would not have been obliged to accept it and judging from his statements, he almost certainly would not have done so.
Offering to leave the Cabinet, however, would have been proper acknowledgement by Smith that he was in major breach of ministerial guidelines in writing an ACC claim-related reference for his friend and National insider Bronwyn Pullar while also holding the ACC portfolio.
Sure, Smith has confessed to "an error of judgment". He also apologised to John Key.
However, avoidance of not just conflicts of interest by ministers, but even perceptions of conflicts of interest is absolutely fundamental to the Cabinet system of government.
The rules in the Cabinet Manual make it very clear that it is not appropriate for ministers to intercede on the behalf of close associates on an official matter, not least because it implicitly puts pressure on public servants to respond favourably to that intervention. There is a word for that: corruption.