Convertibles — that is what the next four weeks are about: prising votes out from “undecideds” or stealing from rivals. So far only ACT of the main five is in full missionary mode, though Labour yesterday moved up a gear.

Minnows have no choice but to go after convertibles. Give United 400 votes an electorate, said Peter Dunne in his television opening on Saturday night, and his “little guy” party would have two MPs to interpose “caring commonsense” between the Labour/Alliance and National/ACT blocks.

The Greens, their brand buried in the Alliance for two elections, have to recover the once-converted. So far they are doing nicely, working a few high-profile issues such as GM foods.

New Zealand First, although in the main five, is also stuck in reconversion, trying to relive 1996 with rambling fireside stories from the one and only Winston Peters.

The Alliance campaign is well-focused, with good catchlines. But, in pitching to give a Labour-led government “heart”, the Alliance is fishing from Labour’s pool — affirming left votes, not converting new ones.

All parties, especially Labour and National, must affirm their core votes or risk losing them to raiders.

National’s television opening was heavily of that ilk, with only a lick or two at the policy items (unions, tax) by which it aims to frighten people from the left — though it does also have catchy negative billboards masquerading as Labour’s. Labour’s opening, though classier, was also heavily affirming, focusing on strugglers already pretty much in its bag on social or small business assistance grounds.

ACT, uniquely among the main five, is wholly in converting mode, aiming both at Nationalists “frustrated” by dependence on riff-raff and, in its treaty, crime and beneficiary policies, at leftward drifters.

ACT has also understood that after 15 years of economic and social upheaval igniting “hope” may be the clincher. It promises “positive change”.

Labour belatedly moved on to that ground at its event launch yesterday with a finely-crafted aspirational speech by Helen Clark, evoking ingredients of “hope”: “trust”, “vision” and national pride. Its small-boy ads are in the same frame.

Mrs Shipley does talk of being “proud”, the slogan on the campaign bus enjoins you to “value your country” and one billboard pushes “trust” — but in the narrow sense of a past record, not broad sunlit uplands. For the moment the real fight is Labour versus ACT.