A scandal can be distinguished from a controversy. Immigration policy became controversial in the 90s, the foreshore and seabed in the 2000s. Even though there were bungles, and offensive views and policies were aired, the underlying issue was always sharp disagreement over core values and policies.

In a scandal, the underlying issue is wrong-doing.

Except when it’s a 'Kinsley gaffe', named after the first political botanist to identify this species in the wild. In these cases, the scandal occurs when a politician says something that is true but they shouldn’t have said, rather than does something wrong. For example, in the mid-2000s the then-Duty Minister Jim Anderton described the US involvement in Iraq as a 'quagmire.' Not only was the truth of this statement known to every politician in the world, it can be seen with the benefit of hindsight to have been objectively completely true. The over-reaction of the US Embassy turned the statement into a minor scandal but it's not clear the scandal caused political damage.

Other scandals that cause little damage or even benefit the party at the centre are the 'You're Nicked, Son' variety where the wrong-doing is so obvious that it's easy for a party to do the right thing. In the 1990s then-MP Michael Laws was caught lying about forging a signature (that of 'Antoinette Beck). His behaviour was so clearly indefensible that his forced expulsion from parliament was immediate, and Winston Peters actually rose in the polls for what was seen as his expeditious handling of the scandal. The recent Maurice Williamson scandal falls into this category.

Then there’s the ‘Bad Smell’ scandals where the underlying issue is one of symbolism rather than substance. It’s hard to identify the wrong-doing but the symbolism ties into a wider narrative that is credible -  ‘this lot are up to no good.’ The scandal then ensnares the party because it can't make something go away - say by sacrificing someone or changing a policy. So the issue rumbles on because it symbolises something about a politician or party. 

The Cabinet Club issue in the news is one of these: At the centre, is a claim that National party supporters paid very large sums to attend dinners where Ministers were present, and talked to Ministers about policy. So far, that is not only within the rules, one of the main ways parties fundraise is by holding dinners or art auctions or debates where donors pay too much and mingle with MPs.  

The Cabinet Club would vault into 'You're Nicked' status if evidence were produced that someone paid money in expectation of a personal policy outcome, and that policy was promoted by the MP or minister. But attending a pricy dinner only amounts to 'cash for access' if there were few other ways to gain access to ministers. It doesn't help that Ministers looked guilty when asked about the events, and misdirected about their involvement. But again that's really a symbol of underlying expectations that this government is evasive and misleading about everything it does. 

The damaging type of scandal that governments fear most is the ‘Slow Burner’ that begins at arms length. Helen Clark had one of those with the Owen Glenn-Winston Peters debacle in 2008, where - in the beginning - there was little she could do to get issues under control. 

Mr Peters claimed not to have accepted money from Mr Glenn and gave her that assurance - she could hardly then have sacked him immediately and brought down her own government, while more and more excruciating facts seeped out. The story became so toxic that Mr Glenn's donation to Labour itself became a scandal, and - combined with controversies over the state's reach (child safety, notorious lightbulbs), the Electoral Act - helped to destroy the Labour government's ability to win the debate about the economy.

In some ways the most devastating effect of a scandal is the distraction it causes combined with the symbolism, which is why the most damaging type of gaffe is often the 'Teetering' scandal that takes weeks or months to unfold, and where the decisive blow never quite appears. Typically the issue begins with either a disputed core fact or a relatively minor one. Tuku Morgan had to resign from parliament in the 1990s, not because he bought an $89 pair of undies with money meant for Maori TV, but because he cracked under pressure over the issue that the undies symbolised. 

The Oravida issue engulfing Judith Collins appears similar to one that surrounded Jenny Shipley when she was prime minister. Then an allegation was levelled in the House that she had a dinner with ad-man Kevin Roberts at which help for the National Party was discussed along with a Brand-New Zealand ad campaign. She could never quite explain what was discussed at the dinner, which led to others filling in the detail for the six o'clock news.

The issue at the heart of Minister Collins' case is whether her status influenced officials on behalf of a company in which her family had an interest. Naturally, if it were shown she did, she would be in a 'You're Nicked' scandal and gone by lunchtime. The oppositions’s problem is that the key facts at the heart of the scandal are in dispute. Her problem, and National’s is that when facts emerge that contradict her account, it looks like a cover up. 

It's sometimes said that it was the Watergate cover-up, not the crime, that brought down President Nixon. This is untrue; he covered up because the underlying issue was that he knew about (or ordered) illegal funding of a crime gang, which broke into his political opponents offices to steal information. Of course that crime would have caused his resignation. ("You're Nicked!") What matters is whether the facts are present to establish an underlying wrong-doing. When the facts are emerging drip by drip the government gets slow-roasted because no single fact on its own is damning, while the overall picture looks worse and worse. 

Meanwhile, the government is knocked off message while it tries to talk up the Budget.

Each new story undermines Minister Collins' credibility among her own peers. 

In the UK they talk about the number of days a Minister can remain in the headlines before they have to resign 'for the good of the party'. Some say five. Some say ten. 

The issue for National now is that the scandal has dragged on for so long that it is engulfing the entire government. If she goes now, the attention will turn to questions of why the prime minister didn't act sooner.

But scandals can work the other way, too: Voters get frustrated with the ongoing attention to something that doesn't affect them directly (this even happened with Watergate). The story becomes so complicated that it's hard to recall why this detail matters (this is how Mrs Shipley eventually got out from under the Kevin Roberts scandal). 

The trick for the opposition is to keep the focus on the scandal - the underlying issue of wrong doing - and not let it become a controversy in which reasonable people can disagree and it all just becomes background noise.

Policy controversy is the engine of democratic politics. People are motivated to participate and support their sides because of their passionately held values and the way those values are expressed in policy. A scandal is an altogether less nobel affair and belongs at the business end of politics.