Just one semi-randomly chosen article, on the Otago Daily Times website, but here are some numbers from it:

A. Don Brash denying allegations or refusing to comment: 4
B. Don Brash distancing himself from views of senior ACT people (incl former): 4
C. Mentions of Don Brash’s failed 2005 campaign: 3
D. Don Brash making an open statement of his position (incl the ad): 2
E. Don Brash attacked by ministers in the government of which ACT is a part: 2
F. Don Brash attacking ministers in the government of which ACT is a part: 1

That, right there, is a party leader under fire.

A is a problem because it shows Brash as weak and evasive.
B is a problem because the fact is that these people are or were his party and its brand — they are what people think they know about ACT. If it turns out they don’t actually speak for ACT, something has to fill that vacuum. This is also indecisive, and because of the nature of the views he is backing away from, weak.
C is a problem because it reminds everyone that they got rid of him six years ago, and why.
D is a problem because Brash hasn’t filled the vacuum caused by B.
E and F are problems because they threaten the integrity of John Key’s National government during an election campaign framed by narratives of unity: the Stadium Of Four Million narrative of the Rugby World Cup, and the Spirit Of The Blitz narrative mandated by the Canterbury earthquakes.

For my money, it’s the last one which is most likely to sink ACT. If Brash doesn’t pull his head in sharpish, Key will be justified in cutting it off. And I reckon he would, sharpish. He’s not called the Smiling Assassin because of his gentle nature and tolerance toward poor performers. And even if Key doesn’t, Brash is up against some powerful stuff in those unity narratives. Nobody wants to back a splitter at a time when Aotearoa is supposed to be thinking and feeling and hoping as one.

L