Here a spoiler alert is needed: should the Prime Minister be reading, he might wish to look away now, or skip to the penultimate paragraph lest he inadvertently see some forensic analysis.
Much of the attention has focused on the Dotcom donation, but it is the evidence about the SkyCity donation that is the more damning. Banks' critics have conveniently ignored evidence that show Dotcom was happy to go along with making his donation anonymous and, in fact, went to some lengths to ensure it could not be traced back. Technically, that donation was anonymous until Dotcom - who also admitted he was disgruntled by Banks' refusal to help him out in prison - got utu by blurting about it this year.
But in SkyCity's case, Banks personally went into SkyCity's offices where a SkyCity cheque in a SkyCity envelope was handed to him by SkyCity chief executive Nigel Morrison. In return, SkyCity was later sent a receipt for the donation. Morrison told police that it was made clear to Banks and Len Brown (his main rival) that the donations were from SkyCity and were not intended to be anonymous.
Banks might not have opened that envelope, but it is hard to believe he did not know it was a donation, and did not wonder where it had gone to when he signed off on the donations return.
While Dotcom might be motivated to give evidence against Banks, SkyCity's CEO has no such motivation. In fact, it would be counter-productive given the reliance on Banks' vote to get a national convention centre.
Key has argued it is not his job to conduct a forensic examination into such matters. Instead, he has brushed off the debacle as unworthy of his attention because it is politically motivated.
That may be true - but Key's defence of Banks is also politically motivated.
Having withdrawn all his own credit from the ATM of credibility, Banks is now relying on Key's. The reason Key has given Banks his pin number is that the PM's eye is on the bigger picture, just as it was with that rather demeaning cup of tea: stability of Government. If sacked, Banks might be docile from the back benches, but it is also possible he would not be. That would endanger a significant portion of the Government's plans, not least of which are its economic plans. Key has gauged that the public interest of maintaining the pre-set course on that front is of greater consequence than losing a bit of self-respect by defending Banks.
Key is now finding out what it was like to wear Helen Clark's shoes when she was Prime Minister in 2008, when her coalition partner Winston Peters was in similar strife over undisclosed donations. Then Key was her interrogator, demanding she ask more questions of the man he called "Labour's sugar daddy", Owen Glenn. Now Key, too, is learning that hell hath no fury like a sugar daddy scorned.
What makes it harder for Key is that Clark had only to swallow back the bile and get Peters through a few months before the election performed its natural cleansing process and saw NZ First sent to the reserves bench for a term.
For Key, it is a much longer period of two years. He has sent an ominous sign to Act about that - warning media this week not to assume that National will endorse an Act candidate in Epsom in 2014.
It was in 2007 that Banks performed his magical self-proclaimed transmogrification to the mayor that cares and shares.
Five years later, Key must now be wishing he had the luxury of being able to transmogrify Banks again from an ostrich into a moa. The moa is also a large flightless bird with one key difference: it is extinct.
