The prime minister is suddenly looking like a throwback to Tony Abbott, health minister, when he was fighting trenchantly against losing ministerial power over the abortion drug RU486.

Driven by the wish to keep the support of Liberal conservatives, on whom his leadership depends, and by his personal moral views, Abbott appears to be digging in against giving parliament a chance to consider same-sex marriage. He would thereby deny his party the opportunity to decide whether this should be a conscience matter for Liberal MPs.

Worse, Abbott is trying to do this by trickiness, suggesting the cross-party bill to be brought forward by Liberal MP Warren Entsch is likely to die the natural death of most private members’ bills. And that is despite giving the go-ahead to Entsch for negotiations on such a bill, and leaving the public impression that he would play fair on the issue. His critics are already seeing it as Abbott going back on his word.

Abbott lost – in a parliamentary free vote and despite using the odd dodgy tactic – over RU486. But the outcome in the same-sex marriage fight is unpredictable.

The stakes are high for Abbott. If the conservatives lose, they would blame him for failing to hold the line. But if same-sex marriage is held off, the Coalition will hand Bill Shorten a useful popular issue for the election. Abbott may think it is marginal, but quite a few people care about it – especially younger voters.

The battle in the next few weeks is likely to be ugly. Senate leader Eric Abetz has kicked off what will be a ferocious campaign from conservatives. He warned of opening a Pandora’s box, in which he sees polyamory residing. With a dig at those who say we live in the “Asian century”, he asked “how many Asian countries have redefined marriage?” He noted the strong grassroots feeling in the party in favour of the status quo – something that would be feeding up to Abbott as well.

Abetz said frontbenchers had a duty to support the present Liberal policy against same-sex marriage. His message was clear to those who could not: he recalled that when in opposition he had opposed the emissions trading scheme policy, “I did the honourable thing and I resigned from the frontbench”.

Much will rest on how ministerial proponents of same-sex marriage – and in the first instance a conscience vote – conduct themselves. They include Malcolm Turnbull, Marise Payne, Simon Birmingham and Josh Frydenberg. Their voices are needed to give some spine to more fainthearted colleagues – MPs who would lean to a conscience vote but are susceptible to scare tactics.

It is ridiculous to say these frontbenchers should resign – not least because it would be a disaster for the government if they did. They will need, but may not have, political courage and a good strategy. In terms of the former, they might take a lesson from Abbott’s sister Christine Forster, who is campaigning widely for change. Forster is both a Liberal and close to her brother. Her position can’t be easy.

Abbott seems, as a first option, to be looking to try to bury the bill rather than gamble on defeating it. “It’s quite unusual for private members’ bills to come on for debate and vote in the parliament,” he said on Thursday. He’s always maintained that a partyroom decision on the conscience question would only arise when a parliamentary vote was imminent.

The government has the numbers in the committee that prioritises legislation to cut the bill off in its early stages. But Abbott would probably find that annoyed backbenchers raised the issue in the partyroom anyway. Would Entsch and fellow Liberal sponsor Teresa Gambaro relish being hung out to dry after they had followed instructions? One way or another, a party room debate seems likely, whatever Abbott’s attitude. Abbott would look more leader-like if he facilitated it.

How the partyroom numbers would fall out on the conscience issue is anybody’s guess; if the Liberals had a conscience vote, the numbers in parliament would still be uncertain.

One argument being invoked – that same-sex marriage is a distraction from the government’s priorities of economic and national security – is a furphy. The political menu has multiple issues; parliament has time enough to deal with them.

A few weeks ago, some Liberals were relishing the division in Labor between those wanting to preserve their conscience vote on same-sex marriage and those saying ALP MPs should be bound. The party’s national conference later this month is due to vote on that.

In one of those embarrassing twists that politics often brings for those exhibiting too much hubris, Coalition MPs find themselves embroiled in a much more serious split on same-sex marriage.

In Thursday’s news conference Abbott said that he could only remember in the 21 years he had been in parliament two or three occasions when a private member’s bill had come on for debate and a vote (his memory was faulty about numbers). Presumably one he remembers very well is that on RU486, which passed in February 2006. He might also recall that John Howard agreed to bring that bill to a vote and allow his MPs a free vote. Howard himself then voted against the bill.

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