If a stern new approach on asylum seekers and the abandonment of a charter of rights hadn’t made it clear enough already, this week’s retreat on an emissions trading scheme has confirmed that this is not a government of a mind to die in a ditch over matters of high principle.

The political problem is not that the policy was unpopular in absolute terms: the most recent Newspoll survey on the question, from February, had 57% of respondents supporting the policy compared with 34% opposed, although this represented a substantial narrowing from a 67-22 split recorded before Copenhagen.

Nor is there reason to believe opposition would be concentrated in electorally sensitive areas. The most recent Australian Election Study found 57.3% support for the proposition that global warming would pose a “serious threat to way of life” among mortgage payers — a decisive demographic element of Labor’s 2007 victory — compared with 48.1% of home owners and 54.5% of renters, who tend to be concentrated in safer and less volatile seats (the respective sample sizes were 597, 754 and 235).

Faced by an opposition leader on the record as saying “the climate change argument is absolute crap”, a government with the courage of its convictions would plainly have something to work with if it chose to engage in a battle of ideas in the context of an election campaign.

However, the concern for the government was that Tony Abbott’s portrayal of an ETS as a “tax on everything” would cut through in a way that a necessarily complex sales pitch about emissions trading could not.

The obvious precedent is the 1993 GST election, in which an unpopular Labor government had only to invoke the spectre of higher prices while watching the opposition flounder as it sought to explain how its reform would work in practice.

Significantly, a Nielsen poll published in February showed respondents favoured the blunter and less sophisticated instrument of a fund to finance the reduction of emissions, as had just been proposed by Abbott, by a margin of 45% to 39%. The backdown on the ETS thus gives the Labor members who won marginal seats at the last election one less thing to worry about.

However, there is another, smaller category of MPs who have reason to see things differently. For Lindsay Tanner in Melbourne, Tanya Plibersek in Sydney and Anthony Albanese in Grayndler, the threat comes not from the coalition on the right but the Greens on the left, and it is on this flank that the government’s recent policy shifts have left it exposed.

The cautionary precedent for these members is Kim Beazley’s me-tooism on asylum seekers at the 2001 election, which fuelled a 10.2% drop in Tanner’s vote, an 8.6% drop in Plibersek’s and a 6.6% drop in Albanese’s, with the Greens gaining most of the dividend in each case. It was then that the prospect first emerged of the Greens overtaking the Liberals on the primary vote and chasing down Labor with their preferences.

A watershed in this respect was reached in the 2007, when Melbourne Greens candidate Adam Bandt surpassed the Liberal candidate during the preference count. However, the decisive point on that occasion was that Tanner’s primary vote was 49.5% — high enough that stray preferences from minor candidates and Liberals ignoring their how-to-vote cards gave him a reasonably comfortable 4.7% win over Bandt. Albanese and Plibersek likewise recorded primary votes of 55.5% and 49.0% that would easily have shielded them against any challenge for the Greens.

Despite opinion polls consistently showing the Greens vote about 4% higher than that recorded in 2007, it seems unlikely that any hit on the primary vote at the coming election would be sufficient to cost these members their seats.

Faced with a choice between a small number of inner-city seats under vague threat from the Greens and a large number of suburban ones under serious threat from the Liberals, it’s not hard to see why the government has made the calculation it has. The bigger question is whether a government without an agenda is willing to expose itself to electoral risk over sacrificing strategy for the sake of tactics.