Much of politics is comparative. Malcolm Turnbull, awaiting judgement from a fickle electorate, told Four Corners that if the Liberals had not changed leaders “we would’ve lost the election very resoundingly”.

It was a sharp, if self-serving, message about how things might have been if Tony Abbott was still in charge. Perhaps unconsciously, Turnbull also highlighted why the Liberals had installed him as leader last September. In many cases, it was not because they believed in his vision or his policies, or because they were personally attracted to his charisma. Rather, they made the ruthless judgement he’d win for them and Abbott would not.

Turnbull is a prime minister on probation. Saturday’s vote will test whether Australians, who for years declared through the polls they wanted him as leader, retain their faith (albeit diminished) in him. And, if he wins, the people’s view will send a message to those Liberals who still accept him only reluctantly. But Turnbull needs not just a win – he needs a good victory to establish his authority with public and party.

His first campaign as leader has looked difficult for him, especially in its early stages. He is not a natural on the hustings. Despite an addiction to trams and trains, in the TV clips his conversations with shoppers often appeared forced when contrasted with footage of Bill Shorten’s down-to-earth style. So much so that Turnbull gave up the street encounters for a time.

At one point a bad cold had him struggling, literally, to get words out. He often looked tired and drawn.

Towards the end, however, Turnbull hit better form. By that stage, he’d learned campaign discipline – not appearing bored, the art of small talk.

But, most importantly, a big break came when the unexpected Brexit decision put new force behind his argument, made throughout the campaign, that people should vote for stability, rejecting not just Labor but protest votes through Greens and independents. The election’s focus sharpened onto the economy, the Coalition’s ground. Labor struggled with its big-spending image. Turnbull seemed to have more bounce; at the same time, he came across as more prime ministerial.

Nine-and-a-half months ago, Turnbull arrived in the leadership partially shackled. He’d ousted Abbott by a fairly decisive 54 votes to 44. But to win support from some Liberal right-wingers, he’d had to agree to retain the government’s conservative climate policy and to stick with Abbott’s plan for a plebiscite on same-sex marriage.

Turnbull looked like he was wearing another man’s clothes. The Nationals distrusted him so much they insisted on the climate and plebiscite undertakings being written into their Coalition agreement with the new leader.

One course for Turnbull would have been to call an election before Christmas, arguing he wanted a mandate. The political attraction was obvious. He was on a roll; Shorten was on the ropes. In November the Coalition, which had trailed Labor consistently under Abbott, was leading 53-47 in Newspoll; Turnbull’s net satisfaction rating was plus 38 to Shorten’s minus 31.

But having finally achieved his lifelong ambition, Turnbull wanted time to govern before plunging into an election, which was due within a year anyway. He exuded optimism, endlessly repeating how we were living in the most exciting times.

Everything seemed possible. The policy “table” was loaded with options, notably for comprehensive tax reform. The new prime minister’s first major policy announcement was on innovation.

Within months, however, Turnbull came to be seen through the sceptical spectacles Australians now don when viewing their leaders. He could never have met their inflated expectations. Contrasting him with Abbott, many had romanticised the leather-jacketed, politically cheeky Q&A performer, falsely believing he would remain that way as prime minister. They were deeply disappointed when he didn’t reverse Abbott policies on the marriage plebiscite and climate.

Then there was the overreach. Turnbull’s decision not to proceed with broad tax reform – partly under backbench pressure, partly because the government couldn’t make the numbers work – raised questions for many about both his commitment to economic reform and his ability to execute it. On Thursday’s Kitchen Cabinet Turnbull admitted that with hindsight he could have done things differently, rather than open the way for his opponents to run a scare campaign.

Shorten and Labor were lifting their performance, striding out boldly on policy in taxation and other areas. Turnbull was losing comparative advantage. By late February, the Coalition and Labor were 50-50 in Newspoll and Turnbull’s personal ratings were sliding.

Within government it was a struggle. Turnbull had won the leadership on the back of the polls; once they fell, so did his internal authority.

Dealing with Treasurer Scott Morrison was frustrating. The ambitious Morrison likes to run his own race, a trait evident in his pre-parliamentary career as head of Tourism Australia. He flagged publicly that he believed in big-bang tax reform, complicating Turnbull’s later pullback. Turnbull was periodically impatient with Morrison and their relationship yo-yoed.

Turnbull has broad pro-market and small-l liberal values; he’s a conservative economic manager, a cautious reformer and a social progressive. He brings to governing a distinctive approach – a belief in agility, being on the balls of your feet and all that jazz – rather than an entrenched ideology. “I’m always prepared to listen to a better argument or a better proposition,” he told Four Corners.

In his last set-piece speech of the campaign, Turnbull said he believed Australians “want our parliament to offload the ideology”.

An element of unpredictability is obvious in how he operates. He’s worked to contain the arrogance and impatience he displayed as opposition leader, but he can be wilful. He’s politically untidy. Colleagues worry about his “thought bubbles”.

I see him as a venture capitalist of politics. Just as he tells entrepreneurs to be bold, follow an idea and if it doesn’t work try something else, that’s how he’s inclined to go about politics.

In a moment of extreme entrepreneurship he proposed, with minimum prior work or warning, that the states might like the power to raise their own income tax. Premiers' jaws dropped before they predictably said no. After their decisive rejection, Turnbull declared that at least things were now clear and moved right on, though he is said to have been a bit jolted by the experience.

Having eschewed an election last year, Turnbull had two choices: wait for the normal time, September, which would mean only half the Senate would face the people, or have an earlier double-dissolution election.

With infinite faith in his ability to persuade, Turnbull had at first hoped recalcitrant Senate crossbenchers would soften after the regime change. They didn’t. Indeed, when he invited them to dinner at The Lodge a couple left abruptly and one complained about the food.

Turnbull became increasingly impatient with this disparate group on whom the government depended to get measures through. Having passed changes to the Senate voting system designed to thwart micro-party aspirants (which in fact they won’t this time), a July 2 double dissolution, launched off the back of the budget, seemed a logical choice.

For technical reasons, this meant an eight-week election, a winter ordeal of endurance to test the strongest of campaigners.

As Turnbull criss-crossed the country during these two long months, the prime ministerial entourage included deputy chief-of-staff Brad Burke; principal private secretary Sally Cray; press secretary David Bold; national security adviser Justin Bassi; senior policy adviser Jon Dart and adviser Pete Anstee. Often Cabinet Secretary Arthur Sinodinos was there and, increasingly, Lucy Turnbull.

Turnbull’s routine has had him out of bed around 5am for a session in the hotel gym (10km on the rowing machine); conference calls with campaign headquarters and the Coalition leadership; a breakfast of fruit, yoghurt and muesli. He consumes black tea early, followed by green tea as the hours wear on.

Each campaign day usually involved two or three events, including a news conference, before, if interstate, the prime ministerial party travelled to the next day’s stop. Behind the scenes were the fundraising lunches and dinners, integral to any campaign.

Abbott’s former chief-of-staff, Peta Credlin, criticised Turnbull for not doing enough media; Team Turnbull believes Abbott did too much. But Turnbull hit the airwaves extensively as election day approached.

Turnbull gambled with keeping his campaign pitch quite limited. He made the budget’s jobs and growth “plan” the centrepiece, with its ten-year A$48 billion company tax cut destined first for small business and later the corporate giants. The budget also included a cutback in the superannuation tax concessions for the rich, which should have been saleable on “fairness” grounds but proved a negative with a disgruntled base.

The emphasis was deliberately on economic management rather than “budget repair”, something Abbott this week said should have received more attention. But “repair” conjures up the prospect of savage measures, which is not a discussion Turnbull wanted to open up just now.

As well as the theme of stability, border protection has been prominent in Turnbull’s campaign. He has pressed it forcefully but, unlike his predecessor, he’s anchored it firmly to the protection of our multicultural society. Mixing the tough with the moderate, Turnbull bundles national security and inclusive unity.

Within the constraints he imposed on himself, the campaign provided some insights into the broader Turnbull. He took a day to attend the historic handover of land near Darwin to Aboriginal owners, and also embraced the interpretation that Australia was invaded by the British. He invited Muslim leaders to a multi-faith dinner at Kirribilli House, a function that landed him in controversy when it was discovered one invitee was on record with homophobic views.

Labor handed Turnbull significant breaks. The Victorian ALP government’s handling of the firefighters dispute enabled him to become champion of the popular volunteers, promising federal legislation.

The biggest free kick, however, was Labor’s admission that in government it would run bigger deficits than the Coalition over the forward estimates. This was a major strategic error by Shorten, who was trying to maximise funds for education and health promises. It was bad even before Brexit, and worse after that event changed the atmospherics.

By the final week, with a big media advertising blitz especially in Sydney and Brisbane, the vibe suggested Turnbull was getting his message out strongly. The previous week, qualitative work done by Landscape Research for the University of Canberra in the Victorian seat of Indi found “soft” voters overwhelmingly favoured Turnbull over Shorten to lead the country.

Tony Mitchelmore, from Visability, whose focus groups this year registered disappointment that Turnbull “hadn’t done anything”, reports that “some people hope he’ll be re-elected and be his own person, get on with things, once he’s got his own mandate”.

Despite the line-ball national polls, those around Turnbull have claimed all along, on their readings of marginal seats, that he would win. An unexpected Labor victory would throw the Liberals into a world of chaos, trash Turnbull and leave the party leadership wide open.

A hung parliament that resulted in a minority Coalition government would be a management nightmare for Turnbull, who is unsuited to tolerating frustrating situations over extended periods.

If, from Turnbull’s point of view, the election is about establishing authority, the question becomes what constitutes a respectable win. To an extent this is in the beholders' eyes. It surely has to be large enough to get the industrial relations “triggers” for the double dissolution through a joint sitting, which would partially depend on the Senate result.

Even with a respectable win, Turnbull would face early challenges in the next term.

The marriage plebiscite would overshadow the first months. Assuming he could get it set up, managing a deeply divided party through a fractious campaign would be extraordinarily testing, especially since Turnbull wouldn’t be above the fray but effectively the most prominent “yes” advocate. If, against the odds, the plebiscite was lost, it would be hard for him to move on from that failed venture.

With all the signs that the Senate will have a large crossbench (aside from the Greens), the upper house could constrain Turnbull’s ability to deliver generally in a new term.

But what exactly would he be delivering? Turnbull would arrive into a second term with a relatively thin agenda and some of that comprises legacy items from the last term, such as the plebiscite and the Indigenous recognition referendum.

Apart from the company tax reduction, modest tax relief for middle earners, the superannuation changes and the continued pursuit of new trade deals, there is little that is major and fresh. In industrial relations there are the double-dissolution bills and a few other items, but not any proposed sweeping overhaul of the system.

Many of the government announcements during the campaign have been dollops of cash for local electoral bribes. The Coalition has yet to spell out what it would do on higher education. A review of climate policy is due but there is no clarity about where it might go. Childcare changes were outlined last term, but are yet to be legislated.

For the most part Turnbull’s personal second-term blueprint hasn’t been mapped out. A re-elected Turnbull would be a potential surprise packet. One source says a comfortable win would give him a “licence to be himself”.

He sounds raring to go. Asked by Annabel Crabb whether it was fun being Prime Minister, he said: “It is the best fun I have ever had in my life. … I’m so happy. I love the job. I love everything about it. I love the ability to do really worthwhile things and to be able to make big changes.”

And what of Turnbull’s own future? A journalist asked this week whether he could guarantee he’d lead a re-elected Coalition into the 2019 election. Once, a question about a prime minister’s future went to the possibility of retirement. Now, it is about the prospect of survival.

“I will be leading the government to the election in 2019 if I am returned as prime minister,” Turnbull said. “You can note that down.”

Not all his colleagues would be as sure. Pushed on Thursday about how he could make such a guarantee, Turnbull conceded “only time will tell”.

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.