For National leader John Key, the events of the week just past may turn out to his advantage, humanising a man who, despite his image-makers' best endeavours, has often seemed wooden in manner and politically lightweight. But right now, he is looking suspiciously like a man who goofed.

The man widely regarded as prime minister in waiting has had a dream run. Recent polls, taken together, have tended to suggest that National could govern alone. No one is pretending that the figures offer more than a pointer towards the result in the only poll that counts, the election: party support tends to harden and become more pragmatic when the votes really matter and it would be a serious mistake for National to take its margin for granted.

Key has not done that. Indeed he has been arguing that National will be the underdog in this campaign. That self-effacing pronouncement is doubtless driven by a measure of tactical cunning - New Zealanders tend to punish contenders' cockiness - but it may be truer than he realises. Key has - or had until this week - scarcely put a foot wrong; but neither had he done much to earn his spot at the top of the polls. Like his predecessor Don Brash, he is still politically green and he faces, in Labour's front bench, formidably experienced opponents who are fighting for their political lives.

Key showed his inexperience this week with not one, but two, blunders: first, he equivocated over his party's position on the Government's move to nobble the sale of 40 per cent of Auckland International Airport to a Canadian pension fund; then he fluffed its position on the Treaty claims process (he now recalls that it was just after he became leader that the party extended, from 2010 to 2014, its target date for the settlement of outstanding claims).

Key quickly cleared up the latter issue, although the former will remain the one that got away. He and his advisers know that, having stumbled at the first hurdle, he was always going to be on a hiding to nothing. He would have been on solid ideological ground condemning the tightening of the rules on foreign ownership as an outrageous intervention in the free market. But the Government move plugs into public unease about asset sales - a subject on which National is historically vulnerable - and there is no electoral advantage in opposing it.

The worst thing for Key is that he dropped the ball with the try line beckoning. The Government's move, plainly tailored for electoral advantage, requires the relevant Cabinet ministers to consider whether overseas investment "will, or is likely to, assist New Zealand to maintain New Zealand control of strategically important infrastructure on sensitive land". Michael Cullen refused to engage in any discussion as to whether the move effectively put an end to the Canadians' bid but, following as it does the retrospective plugging of a tax loophole which immediately diminished the expected returns on their investment, it looks very like a sign saying "Canadians Go Home".

It's hard to argue that there is no case for the Government's move, but the manner of it is exceptionable in the extreme: in changing the rules in the middle of the game, it undermines the country's carefully constructed reputation as a desirable destination for foreign investment and it effectively steals from airport investors who may have been relishing the prospect of fetching $3.65 for shares trading at barely two-thirds that figure. To add insult to injury, Cullen's high-handed and arrogant refusal to discuss the implications of the move made him an inviting target. Key could have pressed home the advantage, condemning the Government's tactics and timing while endorsing the direction. Instead he fluffed his lines.

It may be that we will look back at the end of the year and see a National leader who became, after a false start, more assured in his role. But it may equally be that Key has exposed himself as a man who, in the heat of a hard-fought campaign, will be, like the last National leader, gaffe-prone. What is certain is that the time for rehearsal is past. The curtain is up and there is nowhere left to hide.