Some Liberals love to deride Greens senator Sarah Hanson-Young. In the past, the government’s immigration minister and attack dog, Peter Dutton, was particularly insulting when she was spokeswoman in his area.

Now it’s Hanson-Young, handling the education area for the Greens, who is battling to get her party to pass the schools package that, in political terms, Malcolm Turnbull desperately needs.

The package is a truer version of the original Gonski needs-based system, and so would benefit deserving government schools, which are Hanson-Young’s priority. She’s gone out on a limb within her own ranks to attempt to promote a deal.

The government hopes to have the legislation through this last week before the winter break. “We’ll make sure we land this,” Deputy Prime Minister Barnaby Joyce said on Sunday. The question is: who can it get to be its dancing partners? The Greens, or other crossbenchers?

Negotiations between Hanson-Young and Education Minister Simon Birmingham – one of the better ministers, with an admirably low-key style – have seen the government showing a good deal of flexibility.

Hanson-Young says what the government has put on the table moves the package closer to what the Greens have been advocating.

It involves setting up the independent body to oversee funding that was recommended originally by Gonski, and legislation to tie the states into pulling their weight on money. The negotiations have also canvassed shortening the timeframe of the government’s A$18.6 billion plan from ten years to possibly six years, which could cost the government an extra $4.5 billion-$5 billion over a decade.

The government is coy about the details of concessions it would make to the Greens. But if a deal with those sorts of changes could be done, you’d think the Greens would be trying to clinch it as quickly as possible. It would represent a major win for them.

There is, however, an internal battle – the party is divided.

This is an issue on which one would think Greens leader Richard Di Natale could adopt the more pragmatic style he seemed to promise when he became leader.

Yet on Sunday he showed he was conflicted when he appeared on Sky. Rather than displaying leadership and saying he will urge his party room to accept a deal if it is favourable – which would allow him to claim credit for delivering a better system – he stressed not being hurried and speaking to “all the key stakeholders”, who have in fact already been consulted.

So what’s going on here?

This is going on: the Australian Education Union (AEU) is standing on the Greens’ neck. The AEU wants this as an issue at the election. And the Greens are frightened of the union, especially what it could do to the party’s aspirations in inner city seats.

The teachers’ union has a lot of political clout and there is extensive overlap between its membership and the support base of the Greens. The New South Wales branch of the Greens is strongly identified with the union line.

On Sunday the union position was simply that the Greens must block the legislation this week. It will be lobbying them hard in Canberra over the next few days.

It’s a sordid tale of the power of politics over policy – and it leaves the Greens exposed in their periodic bids to present themselves as the party of principle.

Just as they are responsible for Australia not having a better climate change policy, because they refused to accept the Rudd government’s efforts to put one in place, so too if they don’t cut a schools deal, they will be open to the criticism of trying to stymie the introduction of a more needs-based schools policy.

But if they opt for staying pure – or indeed even if they don’t – the government might get its way via the rest of the crossbench.

These players have demands of their own. But it’s possible a deal with the non-Green crossbench could come at a cheaper price than one with the Greens. If that was the case, the Greens would likely find themselves sidelined.

Meanwhile, Labor’s performance has been hypocritical. It has said all along that because the government’s schools plan fell $22 billion short of the ALP’s original proposals, it wouldn’t even bother negotiating.

As far as one can see, Labor has three motives.

First, it wants to reap the advantage of the discontent in the Catholic system, which loses out in relative terms when there’s a more needs-based system, because it has been feather-bedded with special arrangements by successive governments.

Second, it doesn’t want to allow the Coalition any win on schools policy.

Third, like the Greens it is unwilling to get the teachers’ union offside.

If the ALP really cared as much as it claims about state schools, it would not oppose the government’s policy but promise at the election that a Labor government would top up the money.

But that would be putting policy ahead of politics.

POSTSCRIPT

The Coalition trails Labor 47-53% on the two-party vote for the third consecutive Newspoll – the 14th consecutive one in which it has been behind.

Malcolm Turnbull and Bill Shorten both lost ground on net satisfaction – they are tied in deeply negative territory on minus 23. Turnbull’s satisfaction rating fell from 35% three weeks ago to 32%.

Turnbull has a 13-point margin over Shorten as better prime minister, 44-31%, compared with a 12-point lead in the last Newspoll.

The ALP primary vote is up one point to 37%. The Coalition vote is steady on 36%, for the fifth consecutive time. Pauline Hanson’s One Nation is up from 9% to 11%; the Greens are down from 10% to 9%.