Should one further Brown-instigated or approved favour to former paramour Bevan Chuang, which has an Auckland Council connection, emerge from the woodwork then he has to go.
The same applies to any unauthorised spending or misuse of council funds or resources as a result of their affair.
It had seemed on Wednesday that the Auckland Establishment - the people who will ultimately make the judgment as to whether Brown survives as mayor rather than the long-suffering, run-of-the mill ratepayer - seemed to be almost universally taking the line that his philandering was solely his business as long as it did not affect his ability to do the job. Which, of course, it will given whoever is the mayor is expected to serve as a role model for the city's youth. To reinforce the point, one of his cancelled engagements this week was the annual Foundation for Youth Development Excellence Awards.
Put that to one side. His decision - or that of his minders - to make his one and only media appearance on TV3's Campbell Live was deeply cynical and supremely arrogant. It amounted to another slap in the face for ratepayers who are entitled to expect accountability from their mayor and that he front accordingly.
Campbell did an acceptable job, but seemed more interested in the psychology driving Brown's lapse of judgment and his fall from grace than the ramifications of the lapse.
Brown's performance was astonishing. He veered close to blaming the media for being caught with his pants down. It was almost as if he was telling people off for watching. His apology sounded almost like an afterthought.
Confidence that he would get off the hook, rather than being contrite for what he had done, seemed to be the prevailing principle.
That confidence was misplaced. On Thursday, the revelation Brown had helped Chuang get a council-related job saw the moral compass swing 180 degrees against him.
Auckland Council's chief executive, Doug McKay, wasted little time in doing the right thing in setting up an inquiry.
Inevitably that has taken some of the immediate pressure off Brown to front up to the citizens of Auckland. But it has not reduced the obligations on him to do what is right. Some of his blinkered behaviour this week springs from the underlying and bitter battle between his Labour-aligned camp and the National Party-connected Slater family. But that cannot be an excuse.
Banks, meanwhile, might be grateful that Brown took some of the spotlight off him this week, though not much.
Other than Winston Peters, Banks is probably the country's most complex and misunderstood politician. Beneath his seemingly uncompromising, bully-boyish exterior and populist indulgences lurks a sensible, sympathetic and down-to-earth individual capable of great kindness to all and sundry regardless of political affiliation.
Banks is a refugee from the mainstream. Like Peters, he lives on the edge where trouble comes looking. Is it coincidence that both have faced inquiries into alleged breaches of electoral law and been stood down as minister as a consequence?
When Banks makes a mistake, it therefore tends to be whopper.
That was the case with Banks' passing acquaintance with Kim Dotcom, a relationship the Megaupload founder mistook for friendship. But one which became an embarrassment for Banks. So he cut Dotcom loose.
Banks' bizarre behaviour last year - notably his refusal to address the questions surrounding Dotcom's $50,000 donation to his 2010 mayoralty campaign and the subsequent police investigation into the veracity of his electoral return - may have sprung from guilt.
To confront what he had done would have been an admission of a failure to meet his own perfectionist standards.
Banks' other big mistake was to return to Parliament following a 12-year break.
He wears the tired look of a man out of his time, a lonely and lost soul who knows an ever-younger generation is now calling the shots in Parliament.
Even before this week's Auckland District Court ruling that Banks stand trial on charges he falsified his election return, it was inconceivable he would stand again in Epsom at next year's election.
And not just out of a personal desire on Banks' part to escape Wellington. And not just because he will be nearing the age of 68 when election day rolls around.
Act simply could not sustain what would be another three-year hiatus with Banks as its figurehead. Sure, there have been some achievements under his leadership, the most visible ones set to be the clutch of charter schools timetabled to open next year.
But there is no apparent sign of energy or momentum driving any fresh initiatives beyond what is contained in the two-year-old confidence and supply agreement with National.
Instead, there is the new distraction of court battles well into election year as Banks ponders whether to appeal the District Court's ruling.
The smart thing for Act to do would be to persuade Banks to give up the party leadership and hand it over to whomever the party chooses as its fresh candidate for Epsom.
That ideally would happen early next year, allowing the new face time to get established in the seat with the hope National will once more come to the party with an electoral accommodation.
Such a strategy would allow Banks to fade out of the picture and possibly enable his court appearances to be quarantined from Act's efforts to rebuild its near-bankrupt brand.
It would also fill the vacuum if Banks was convicted and had to resign from Parliament. However, if he is found not guilty or wins an appeal which blocks a trial, he will claim redemption - something that would make it unlikely Banks would exit the political stage before he was ready to do so.
