They have been locked together in combat for almost three decades, after being acquaintances much earlier, since the formation of the Australian Republican Movement in 1991 and Australians for Constitutional Monarchy in 1992. Turnbull was a founding member of ARM and became its second chairman in 1993. Abbott became the first national executive director of ACM. He entered parliament in 1994, a decade before Turnbull, while the latter led the ARM right through to the republic referendum in 1999. Abbott was a major figure in the 1999 'No' campaign and is particularly associated with the slogan "Say No to the Politicians' Republic".

That long connection has become front of mind again through the excavation of Turnbull's negative views of voluntary postal ballots. He once regarded them as seriously flawed. The context was their use in elections for delegates to the 1998 Constitutional Convention, which was being contested by Turnbull's ARM.

The Abbott-Turnbull connection has also been elevated by Bill Shorten's promise of a republican plebiscite in Labor's first term of office if he wins the 2019 federal elections. Abbott immediately railed against Shorten's proposition, knowing that the republican Turnbull differs from Shorten only on tactics and strategy about how to bring about an Australian Head of State.

Abbott's determination to have a same sex marriage plebiscite, the process which he engineered in 2015, also recalls his approach to fighting against the republic referendum. Then he campaigned on the slogan, "Say No to the Politicians' Republic". Now, although to my knowledge he has never used the phrase, his negative campaign slogan is effectively "Say No to the Politicians' Same Sex Marriage Reform". His opposition to a parliamentary conscience vote has some consistency about it.

Abbott and Turnbull are famously divided not just on the republic and same sex marriage but also on climate change. The chasm between them is built on this trifecta of issues, but reflects many others because these three reforms share a view of the world, between the modern and the traditional, between the status quo and reform. They stand firmly on different sides of a big divide.

They have tackled one another on numerous occasions. The first big one since the republican clashes in the 1990s was in 2009, when Abbott brought down Turnbull to replace him as opposition leader after Turnbull, 10 years Abbott's parliamentary junior, had reached the top job before him in 2008. That successful challenge rested on their different approaches to the urgency of climate change.

Six years later, biding his time, Turnbull deposed Abbott as Prime Minister after the latter had dug a huge hole for himself. Now Abbott is grimly determined to lock Turnbull into a conservative agenda and to undermine his leadership. The first of these aims is often forgotten in the speculation over whether Turnbull will survive.

In all the controversy about plebiscites, compulsory or voluntary postal, what will be crucial is how both Abbott and Turnbull campaign during them. The spotlight will be on them for several months. And both will badly want to win.

Abbott's campaigning record against the republic, against Labor prime ministers, and most recently against Liberal opponents within his NSW branch, demonstrates that he will throw himself into a hard-nosed and dramatic campaign. As a most successful opposition leader he will be one of the most feared leaders of the NO campaign during the plebiscite. Yet for his own dignity and survival Turnbull must manage to beat him on this occasion.

Turnbull's natural style is very different and markedly more restrained. During the last federal election campaign he was not as comfortable on the hustings as Shorten. As the Prime Minister he will also be constrained by the expectations of his office to be dignified. This time he and Shorten will be on the same side and will presumably collaborate in framing the YES campaign. Turnbull can't afford to stand back.

If there is eventually a parliamentary conscience vote during this term how Turnbull carries himself in the lead up will be equally important. The role of a leader can be crucial in conscience votes because it is not just a case of individuals having a free vote. MPs still look for cues about how to vote and what their leader is doing makes a difference. Leaders can still exercise implicit authority and persuasiveness by sending out strong signals about how they themselves will be voting. The same applies to Abbott.

The long Abbott-Turnbull era continues for now. There is a fascinating uncertainty about how history will judge the lives and careers of these two men in the years to come. The final judgement will be both on the individuals concerned and on the culture wars of the past 30 years. If Abbott comes to be ranked as the more significant of the two then it will be a sign that the status quo has prevailed on many issues and that Turnbull has been on the losing side.

But if Turnbull emerges as clearly more significant then constitutional reform, climate action, and same sex marriage will have won the day and Australia will be very different. Then it will be a case of untangling the many positive aspects of Turnbull's contributions from those of other advocates.

John Warhurst is an Emeritus Professor of Political Science at the Australian National University