He divided a movement. Majority support, once strong, is no longer assured. He is the prime minister who broke this nation’s heart.

John Howard and the republican referendum?

No, Malcolm Turnbull and marriage equality.

Oh, the irony. The depressing, excruciating irony.

Consider the similarities.

Polls told us back in the late 1990s that the republican movement enjoyed majority support. Polls tell us today that marriage equality enjoys majority support.

History tells us that using tactics and process to divide a movement is effective at defeating it. Howard divided the republicans over questions of model – direct election vs. parliamentary selection of the president. Turnbull is dividing supporters of marriage equality over the process – plebiscite vs. parliamentary vote.

Here’s the difference: Howard was not a republican. It’s hard to judge him too harshly. A scorpion does what a scorpion does. A politician using political tactics to defeat his political opponents is not new.

But Turnbull tells us he is in favour of marriage equality. Yet now that he is the prime minister he’s using Howard’s tactics with little thought for the consequences. No one – including Turnbull – should be surprised when marriage equality ends up in the same place as a republic: defeated at the ballot box in a plebiscite and off the agenda for years.

This is most likely exactly what certain Coalition MPs had in mind when proposing a plebiscite on same sex marriage.

Turnbull is all over the shop when it comes to relying on a public vote to deliver significant legal and social change. On the one hand, he is incredibly alive to challenges: publicly and in conversations with the Referendum Council advising on constitutional recognition of Indigenous Australians, Turnbull is constantly reminding that success is difficult and should not be taken for granted. Polls indicate that upwards of 85% Australians support constitutional recognition – and yet Turnbull is rightly quite concerned that Australia only holds a referendum if and when it can succeed.

As Turnbull says, the only successful referendums have been ones that were “uncontroversial and had little to no opposition.”

On the other hand, Turnbull seems an absolute Pollyanna when it comes to a same sex marriage plebiscite – despite the fact that the issue is controversial and does have opposition. On Sunday he told the ABC Insiders program:

There is no question that the fastest way, the way you guarantee that there is a vote in the parliament on gay marriage – in this parliament – is to support the plebiscite. Personally I have no doubt the plebiscite will be carried, and the same sex marriage legislation will sail through the parliament.

Technically speaking, the fastest way to guarantee a vote in the parliament on gay marriage is if the prime minister brought forward a bill on the subject and let his party room have a free vote. No plebiscite is needed to give the parliament permission to have a vote.

I have previously supported a plebiscite, if for no other reason than there seemed to be no other way to advance the cause.

But the longer the debate drags on, the more difficult it becomes. If anything, look at the campaign for constitutional recognition. It’s an initiative that’s been formally underway for nearly a decade: expert panels, Senate reports, a taxpayer-funded campaign and now a Referendum Council (of which I am a member). Yet the longer it takes the more out of reach the goal seems. Expectations are raised and frustrated, opposition becomes entrenched, and events overtake the original idea.

If we’d had a marriage equality plebiscite within a year of Tony Abbott’s original proposal, I think there would have been less angst and fear, more hope and momentum, and (maybe) more civility. But now the issue is growing more politically charged and the same infections that beset constitutional recognition – expectations, fear, weariness, anger and other events – risk contaminating the debate on marriage equality.

Turnbull, of all people, should not be so sanguine about succeeding with a “yes” vote at a marriage equality plebiscite. There’s a lot of support for same sex marriage, but there’s a soft middle in that support that will be vulnerable to a “no” campaign. Some people may not be fussed if same sex couples marry, but those same people might not be fussed enough to rouse themselves on a Saturday to go vote for it – especially if their vote isn’t binding on MPs. With the likes of Cory Bernardi suggesting he will not consider himself bound by a “yes” result, why bother to express your view in a plebiscite if your senator or local member is going to ignore it anyway?

But Turnbull should be well aware that his Howard-esque divide-and-conquer tactics pose the greatest danger to the “yes” vote getting up in a plebiscite. Already supporters of same sex marriage are splitting: Australian Marriage Equality convenor Rodney Croome has resigned, for good reasons and in good conscience, to fight the plebiscite. Michael Kirby , Dr Kerry Phelps and Patrick McGorry raise legitimate concerns about the legal, emotional and mental health consequences of a plebiscite. The Greens are going to oppose the enabling legislation and Labor looks inclined to do the same.

If the plebiscite does get up, a movement divided by the prime minister’s political tactics will need to unite for a “yes” campaign. Malcolm Turnbull should know how that is likely to end: he will be the prime minister who broke the nation’s heart.