He's now been Labor leader for longer than Paul Keating. It may not seem like much, but in recent history, being Labor leader is one of the most precarious jobs going in federal politics.

At four years, three months and seven days, Shorten's lasted longer than not just Keating but Kevin Rudd and Julia Gillard (who each made about three years), Simon Crean (two years) and Mark Latham (one year). Only Kim Beazley, who had the job for five years in his first stint, has been leader for longer than Shorten in the days since Bob Hawke.

In 2018, Shorten could also be on the cusp of another, much bigger achievement. It's possible that by the time the footy finals roll around in late September, he will be prime minister.

With the next federal election on the cards sometime between next August and May 2019, Labor has enjoyed a clear, winning lead in the polls for well over a year. In December, both the Fairfax-Ipsos poll and Newspoll had Labor in front, 53 per cent to the Coalition's 47 per cent. This week, the Guardian Essential poll posted the same result.

And yet, is Shorten a shoo-in for The Lodge? As he enters what could be the final stretch, he remains decidedly unpopular with voters. In December, the Fairfax-Ipsos poll had 38 per cent of voters approving of his performance, with 52 per cent disapproving, giving him a net rating of -14 per cent. The last time he was in positive territory (with a measly 10 per cent) was in January 2015.

After Labor lost the Bennelong byelection in December, reports emerged that Shorten had hurt his party's chances in the Sydney seat. Meanwhile, Labor's tightly held internal assessment of the 2016 election reportedly found it would have won had Shorten been more popular.

This comes as Shorten faces an unpredictable few months. Thanks to unresolved citizenship questions, there could be as many as four byelections for sitting Labor MPs. David Feeney in Batman, Susan Lamb in Longman, Justine Keay in Braddon and Josh Wilson in Fremantle are all sweating on further High Court rulings.

Of these, Feeney is in real strife, with Labor insiders predicting he (or any other Labor candidate) will not survive the growing Greens vote in the inner-Melbourne electorate. Lamb's margin is less than 1 per cent and in Tasmania's Braddon, Keay is vulnerable to a Jacqui Lambie challenge.

Is Bill headed for a "killing season"?

In mid-2017, Ipsos conducted focus groups with undecided voters in Sydney and Melbourne. Some of the descriptions of Shorten included, "he stabs people in the back", "a snake", "inauthentic", and "sorry but I can't stand him".

Turnbull may be suffering in the polls (his personal ratings as of December were at a lowly -7), but the Coalition sees a major opportunity in Shorten's unpopularity. Witness the Prime Minister heckling Shorten in the last question time before the Christmas break: "The Leader of the Opposition never even bothered turning up [to the New England byelection campaign], not that he should have, because he's not very popular up there."

As the political year begins in earnest, expect to see the government make as much mileage as it can under the banner of "trust". It's an ongoing weak spot for the Labor leader.

Even though Turnbull himself deposed a first-term prime minister, the first time many voters became aware of Shorten's Canberra career was during his "faceless" involvement in Rudd's demise in 2010. Three years later, he was also instrumental in swapping from Gillard back to Rudd. And while Shorten, as head of the Australian Workers' Union, was lauded for his leadership during the Beaconsfield mine disaster in 2006, his union career has since become fodder for his enemies, who like to paint him as a purely political animal.

Contemplating the year ahead, one Labor insider sets out the armageddon scenario: If there are byelections and the results are bad for Labor and then a leadership alternative like Anthony Albanese "goes feral", the first quarter of 2018 could be Shorten's "killing season".

And yet when questioned over Shorten's hold on the job, Labor MPs scoff at the idea there could be a change of leader. Says one Labor MP – not known for their ardent support of Shorten – "it's not a live option".

There are a number of reasons for this. Firstly, there is the structural: under changes introduced by Rudd in 2013, it is a lot tougher to change Labor leaders than it used to be. Not only do both federal MPs and the party's membership now get a say in the leadership (requiring a campaign and a postal ballot), but 60 per cent of the caucus has to agree to have a leadership spill in the first place.

"It would be catastrophic. You couldn't do it quickly or cleanly," another MP says.

Then there is the historical reasoning: Labor MPs who entered Parliament in 2013 and 2016 (who make up about 40 per cent of the caucus) are very serious about not repeating the mistakes of their predecessors. Those who lived through the Rudd and Gillard coups have no desire whatsoever to return to those days. Everyone also knows it would be electoral poison.

Finally, there is the logical take: while Albanese, deputy leader Tanya Plibersek and shadow treasurer Chris Bowen are all suggested as possible successors, none are currently seen as game-changing alternatives, worth the pain and mess of a leadership spill. Indeed, getting rid of your leader also seems very silly to contemplate when you are track to win the next election and win convincingly.

"Shorten has been underestimated"

Shorten, however, is well used to predictions that his political career has peaked.

"Bill Shorten has been underestimated continually by the Canberra [press] gallery since his election," says Labor frontbencher and Victorian Left faction powerbroker, Kim Carr (Shorten is a member of the Right faction).

Shorten, who won the caucus vote but not the membership vote to defeat Albanese for the leadership in 2013, was never supposed to last. He was not the popular candidate, he was taking over a party that had torn itself apart and he himself had been up to his neck in all the drama.

Then he wasn't supposed to survive the royal commission the Abbott government launched into trade unions in 2014 (which saw Shorten questioned over his time at the AWU). Just as he wasn't supposed to survive Turnbull's ascension to the prime ministership in 2015.

But Shorten has a knack for hanging on. One Labor insider notes that when Shorten came to Canberra in 2007, Rudd gave him a supposedly low-profile, junior portfolio in disability services to bury his career. "But he turned it into the NDIS."

Shorten skeptics argue he has only maintained the leadership because of Abbott's mistakes and now Turnbull's disappointing performance. But others say the Labor leader deserves credit for doing what once seemed impossible: uniting the party and coming very close to winning the 2016 election.

Bowen notes that while the Rudd-Gillard days "seem like a long time ago, it's not".

Whether consciously or not, when asked to talk about Shorten's strengths as a leader, Labor MPs describe him as a sort of anti-Rudd (who was infamous for his temper and chaotic leadership style). They talk about Shorten's collegiate approach, of giving frontbenchers space to work in their portfolios and his ability to take advice from different quarters.

"I couldn't ask for a leader who backs my ideas as much as Bill," Bowen says, pointing to Shorten's support for Labor's controversial negative gearing reform in the lead-up to the last election. "Most leaders would run a mile from that."

Frontbencher Terri Butler says Shorten's office is easy to talk to, and that "information flows". Carr adds: "He's not abrasive in his personal style."

Executive director of the John Curtin Research Centre and secretary of the ALP's national policy forum, Nick Dyrenfurth, has previously been an advisor to Shorten. "He is probably the best boss I've ever worked for. He was sympathetic, always mild-mannered, his work ethic was quite extraordinary."

Others cite his ability to listen, rather than prove how much he knows about a given topic, as a major strength.

Unpopular. But so what?

The Australian National University's election study asks voters to rank the likeability of leaders on a scale of 0 to 10. According to the 2016 report, Shorten was rated the lowest of any opposition leader since the late 1980s (with 4.22), barring Andrew Peacock in 1990 (with 3.87). Yet, he was also close to Abbott's score when he won the 2013 election (4.29) and Turnbull's in 2016 (4.94).

Executive director of Labor-aligned think tank Per Capita, Emma Dawson, cautions Shorten's unpopularity should be seen in the context of a general decline in trust in political figures, adding unpopularity is not always a barrier to success. "Nobody loved John Howard," she says.

When asked specifically about Shorten's lack of popularity, Labor MPs concede he is not the kind of "inner-city intelligentsia" type that appeals to political commentators. Other political watchers note his communication style can be "daggy". But MPs argue he is good at meeting and talking to people in real life. They also argue opposition is a tough gig: you don't have money to spend, a bureaucracy to support you or the amount of media coverage the government enjoys.

"It's very rare for an opposition leader to be preferred prime minister," says Bowen. "You become prime minister and then become 'preferred prime minister'".

Looking ahead, the party is placing its faith in the "bread and butter": if Shorten concentrates on policy areas like cost of living, wages, jobs, health and education, this will trump the personality stuff, or so the thinking goes.

Not that there haven't been efforts to improve the way Shorten presents to voters. While he keeps punching out the press conferences, he has also done about 60 town hall meetings with voters – where he can play to his strengths as a campaigner – over the past two years.

A regular exercise regime (begun for health and thinking time) has seen him lose a significant amount of weight in recent years. And he doesn't rely on the cringe-inducing one liners ("zingers") as much. His recent hiring of former Fairfax press gallery photographer Andrew Meares as a digital communications adviser should see his image become more slick and sophisticated in what could be the most important year of his career.

Shorten's wife, Chloe, is also seen as a huge asset, and has been doing more to boost her profile. Last year she wrote a personal book about blended families (she has two children from a previous marriage). This April, she's due to release a cookbook.

Over Christmas, Shorten had three weeks off and road-tripped from Melbourne to the New South Wales south coast with his family. It was a chance to reset after a messy end to 2017, which featured Sam Dastyari's resignation, the Bennelong loss, the citizenship debacle catching up with the ALP, and some factional unhappiness in NSW and Victoria thrown in for good measure.

This week, Shorten was back at work, holding strategy meetings for the year. One of his first major events will be a speech at the National Press Club on January 30.

The big challenge during what promises to be a tricky time will be to try and ensure Labor, and Shorten himself, are not the main story.

As one Labor MP hopefully notes: "our good periods [in opposition] have all coincided with us having something meaningful to say".