National will be betting that bark doesn't translate into a bite - and if Key's endorsement isn't enough to stop it, the poll trends might.
National supporters can afford to be recalcitrant in Epsom while National is on track to get a majority.
But National has started slipping and its votes are going to a far more dangerous home than Act. They are going to NZ First.
The Herald's recent DigiPoll survey showed much of the lift for NZ First came from those aged over 60 deserting National for NZ First. NZ First has also started targeting National voters who might be open to seduction. Key might pride himself on leading a moderate, balanced Government, but his party supporters are a broader church. So Peters' main messages have been aimed at chipping away at those on the edges - railing against the partial asset sales policy that has upset Grey Power, re-treading his one-law-for-all cry against "separatism" - a line also peddled by Act's Don Brash - and an attack on the emissions trading scheme.
But while many National voters may not be impressed with Act, even more are unimpressed with NZ First. So the higher NZ First gets at the expense of National, the more those Epsom voters will start to find they are not unhappy about voting for Banks.
In such a situation, Epsom voters are likely to take the better-safe-than-sorry approach. Yes, Act's present polling may show it will get only one or two MPs in - but those one or two might well be critical if National is to maintain its position of being able to pass legislation with the support of only one of its coalition partners.
In a further irony, NZ First's rise in the poll is good news for another of its enemies - those campaigning against MMP.
The Vote for Change group has used Winston Peters on its billboards as its chief bogey man to scare people off MMP.
Until recently, the actual return of NZ First was hypothetical. But for each decimal point it goes up the poll, the closer the bogey man goes from being a nightmare to jumping out from under the bed.
Until now, the polls have shown MMP gradually taking a lead for the upcoming referendum. It may be that the reminder of Peters puts people off.
Supporters of MMP have been done a favour by the absence of Peters from Parliament for the term preceding the referendum, and by the National Government's decision to sign up with both Act and the Maori Party.
The internal turbulence of both of those partners has not impacted on the stability of Government as a whole.
National was partly relying on a public wariness of throwing that aside at a time of uncertainty.
Then along came Winston and four polls showing he was on the rise. National-aligned blogger and pollster David Farrar has estimated Peters needs a further 50,000 votes to get to the 5 per cent threshold from the polls' average of 3.2 he is at. Peters got more than halfway to that 5 per cent on minimal publicity.
That will increase, and on Wednesday, his efforts have gained him a place on the TVNZ minor party leaders' debate. Nobody knows how it will end. Whatever you do, don't fall asleep.
