For the second time in the campaign, Tony Abbott has been dropped in it by a frontbencher. Scott Morrison plainly had failed to work through the implications of the Coalition’s immigration policy, and the direct result was Abbott thrashing around yesterday and last night on The 7.30 Report attempting to free himself from it.

The essential problem is that the Liberals insist they’ll cut immigration, but can’t explain which categories they’ll cut. It’s a sort of demographic version of “Government waste” — the inevitable claim that every Opposition makes at every election that many millions of dollars are available to fund programs by cutting back “Government waste”, a convenient expenditure reduction that will offend no one.

Morrison himself struggled with it yesterday in an amusing interview with ABC Newsradio in which he couldn’t bring himself to admit that yes, New Zealanders would be one of the possible targets for exclusion under the Coalition policy. Morrison twisted every which way to avoid referring to the Land of the Long White Cloud.

I know Australian election campaigns have stooped to some pretty low depths over the last decade, but now we’re picking on New Zealanders?

The essential problem for Abbott was shown when Kerry O’Brien pressed him to explain where exactly cuts would be made. “Look,” replied Abbott, “I just can’t specify every last category at this point in time.”

Labor are belated converts to the issue of sustainable population. So, judging by Abbott’s enthusiasm for a big Australia until recently, are the Coalition. Clearly the Liberals, who had assumed they owned the issue and could use it at their leisure during the campaign, were surprised by Julia Gillard’s emphasis on the issue last week and scrambled to react. In doing so, they’ve produced a half-arsed policy that doesn’t withstand the slightest scrutiny.

Abbott also wandered into dangerous territory when he was asked to reconcile his sudden dislike of population pressure with his enthusiasm for higher fertility. He ended up taking a leaf from Julie Bishop’s book and quoting Paul Keating from 1969 to the effect that Australian babies were the best immigrants (what does that even mean anyway?)

This lays bare the cynicism at the heart of both the Liberal and Labor pitches on immigration. Julia Gillard and Tony Abbott can’t be for a sustainable population and for higher fertility at the same time. More people are more people, whether they’re born here or they flew here. You don’t cause less congestion or take up a smaller seat on the bus if you’re Australian-born. And immigrants arrive here ready to go to work. Kids take two decades of rearing and educating before they’re ready to start making an economic contribution.

So why are the Labor Party and the Liberal Party singling out immigrants?

You know why.