John Armstrong: Brethren blunder a spin doctor's worst nightmare

This is the kind of lapse on which an election can turn. This is a spin doctor's worst nightmare.

Don Brash has made a blunder of monumental proportions at the worst possible time for National.

And for him. It may prove to be the difference between him becoming Prime Minister or not.

He was offered every chance all this week to come clean about National's contacts with those members of the Exclusive Brethren sect responsible for distributing the now-infamous pamphlet which grossly distorts Green Party policies.

He instead ducked questions. He issued denials to others.

He is now complicit in a cover-up.

His credibility takes a consequent ravaging.

A week out from election day and with the polls switching back in Labour's favour, he has been found wanting on the most fundamental test of leadership - whether he can be trusted.

How much damage has been sustained by National is more difficult to assess in such a fast-moving campaign.

But the momentum the party had begun to generate has come to a shuddering halt.

The wisest thing would be to admit to an error of judgment and apologise. Toughing it out could mean limping to defeat.

He has devalued his worth to National. He has been revealed to be the one thing the voting public had earnestly hoped he was not - just another politician willing to countenance dirty tricks.

Had he issued his denials as prime minister, he would have been gone - and long before lunchtime.

Was it naivete that prompted his belated admission yesterday that sect members had told him they were going to distribute the offending pamphlets?

Or was he worried someone would spill the beans? Or had he suffered yet another memory lapse?

These are excuses, not explanations.

Voters will feel National has treated them like fools. National pleaded innocent to charges that it knew what was going on. National thought it could get away with giving a nod-and-a-wink approval of a $500,000 covert operation discrediting Labour's principal ally. National has been found out.

Helen Clark has put the issue of "trust" at the forefront of Labour's campaign, constantly querying whether Dr Brash can be trusted not to resuscitate an extreme right-wing policy agenda once he gets into Government.

At times, Labour's attacks on Dr Brash have undermined this strategy. Labour has not been sure which Dr Brash it should present - the New Right ideologue with a ruthless hidden agenda or the inexperienced but essentially harmless Mr Magoo-like bumbler who will not be able to cobble together a government anyway.

The terse Dr Brash seen on television news last night will shock those voters who think he is closer to the latter - and that is to Labour's advantage.

Until now, Dr Brash's stumbles have had no material effect on his standing.

But it was always the case that one too many mistakes would suddenly tip the scales against him and sympathy for his inexperience would evaporate.

If this lapse does not do it, nothing will.