SYDNEY - With a wide triumphant smile, Australian Prime Minister Malcolm Turnbull marched through the stately grounds of Government House in Canberra, where the Governor-General had given royal assent to the newly-passed same sex marriage laws.

Asked by a television cameraman how he felt about the end of the year, Mr Turnbull said confidently on Friday (Dec 8): "It's a great finish."

Mr Turnbull could be forgiven a moment of glee. He had just survived the so-called "killing season" - the final sitting week of Parliament, in which embattled leaders in Australia tend to be ousted by their parties.

In recent weeks, there has been much speculation about whether Mr Turnbull will be the latest Australian PM to be turfed out.

Mr Turnbull himself toppled former Coalition leader Tony Abbott in 2015. This followed Labor leader Kevin Rudd's ousting of Julia Gillard in 2013, three years after she unceremoniously toppled him in the first of Australia's recent - and destructive - series of political coups.

For the first time, opinion surveys have shown Mr Turnbull slipping behind Foreign Minister Julie Bishop as preferred prime minister. A Fairfax-Ipsos survey on Dec 3 found 32 per cent of voters supported Ms Bishop, compared with Mr Turnbull on 29 per cent, Mr Abbott on 14 per cent and the remainder preferring other contenders.

Surveys show the Opposition Labor party has remained ahead of the Coalition since September 2016. A Newspoll survey on Dec 4 found that 53 per cent of people prefer Labor, compared with 47 per cent support for the ruling Liberal-National Coalition.

These dire survey results have led to frenzied speculation about Mr Turnbull's future.

But the question being debated by analysts is whether the Coalition will be willing to dump yet another Australian leader, given that the recent trend has shown that internal party-room coups lead to only short-term gains.

The problem with such coups is that they present the government as unstable and leave behind embittered former leaders - such as Mr Abbott - whose continued presence in Parliament looms as a constant threat to the PM.

The last Australian leader to avoid being ousted - former Coalition Prime Minister John Howard - warned that it would be "madness" to dump Mr Turnbull.

"Another leadership change, in anything other than the very short term, would do very significant damage to the Liberal Party and government," Mr Howard told The Australian newspaper on Dec 1.

He added: "The best option for the Liberal Party is to help make Turnbull's leadership work and succeed. In my view, he can still be successful."

But these final words seemed to recognise that, on his current course, Mr Turnbull faces a looming defeat at the next election, due by 2019.

It has been a stark turnaround.

A former merchant banker and self-made millionaire, the 63-year-old was once one of the country's most popular politicians.

He was admired for his eloquence and his mix of progressive views on climate change and social issues such as same-sex marriage, combined with more conservative views on economics.

But his standing has plummeted since 2015.

Fearful of right-wing elements in the Coalition, he weakened his support for strong action on addressing climate change and overcame his previous opposition to a national postal vote on same sex marriage.

Last Friday, he announced that he was setting up a royal commission into Australia's banking sector. This marked yet another embarrassing backflip for the pro-business PM, who had previously staunchly rejected the Opposition Labor party's call for such an inquiry. But he was forced into the move by several rural-based MPs in his Coalition, who wanted greater scrutiny of the banks.

All this has occurred against the backdrop of the embarrassing dual citizenship saga. So far, nine MPs have been forced to leave Parliament after it emerged that they held a foreign citizenship, which is barred by the constitution. Numerous other MPs face questions about their citizenship status.

The saga was not Mr Turnbull's fault but - as leader of the country - he appears to have incurred much of the blame. It did not help that he was slow to respond and appeared to be forced into ordering an audit, which required all MPs to reveal details about their citizenship status and family histories.

Perhaps the strongest argument in favour of Mr Turnbull's leadership, according to analysts, is that there is no clear alternative.

In a story headlined "Malcolm Turnbull can breathe easy: this will be a killing season without a killing", Fairfax Media commentator Peter Hartcher said that possible alternatives such as Ms Bishop have no intention of launching a challenge.

"They've seen the deep, enduring damage that a leadership coup inflicts," he wrote on Dec 2.

"If you want to replace the prime minister, you have to have a replacement. There isn't one, not yet."

And so the killing season ended with a joyful Mr Turnbull enjoying the legalisation of same-sex marriage - a historic change that prompted national celebrations.

He will survive into the new year, which will yet bring a further round of killing seasons.