The government has built a bonfire of embarrassments - and the Wentworth by-election looks set to set it aflame

• The by-election for former PM Malcolm Turnbull's Sydney seat of Wentworth is on today

• Astonishingly, even new PM Scott Morrison has conceded that the Liberals could lose the seat for the first time in history with the biggest swing in a by-election in history

• A shambolic week for the government has further damaged the chances of the Liberal candidate, Dave Sharma, retaining the seat, meaning the government could lose its one-seat majority.

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If money talks in the same way politicians leak, then the Liberal Party is less than 12 hours away from losing Malcolm Turnbull's seat of Wentworth for the first time in its history.

As voters head to ballot boxes in Sydney's eastern suburbs today, punters have thrown their support behind independent Dr Kerryn Phelps, who two days ago jumped ahead of Liberal candidate Dave Sharma as the favourite on betting markets.

It's an astonishing turnaround in a seat that never should have been in doubt for the Liberals.

The odds in favour of the AMA boss shortened again yesterday, down from $1.65 to $1.33, while Sharma's lengthened from $2.15 to $3 according to Sportsbet.

But the betting market's not alone

Three days ago, perhaps in a strategic effort to rouse complacent Liberal supporters, The Australian was leaked polling that had Phelps ahead of Sharma 55% to 45% on a two-party-preferred basis.

That's a swing of more than 27% - Turnbull had a margin of 17.7% - and even in these politically volatile times (in September, the NSW state seat of Wagga Wagga saw an independent take the seat from the Liberals with a 22.5% swing), it will be the biggest swing in by-election history if Phelps wins.

But interestingly, the polling supposedly found that 75% of the electorate believed the government would retain the seat, and one unnamed Liberal was quoted as saying “We are being killed by the expectation" of a win.

So today's vote in Sydney's affluent yet surprisingly diverse eastern suburbs is now seen as a key litmus test on the future of Morrison's fledgling leadership. Losing Turnbull's seat would be just another sign of a Coalition government in terminal decline, a demise hastened by the party's August ousting of the former PM.

The Liberals have a self-inflicted wound that's now turning septic. To go from a sitting MP with nearly a 68% primary vote, which Turnbull had, to the likelihood that Sharma's primary vote won't get above 40%, the level many believe is required for him to win the seat, is a logic-defying achievement.

Wentworth voters, already irritated by the loss of their popular MP and Prime Minister, have been offered little by way of reassurance from the Liberals during the campaign. As the party's desperation became more palpable when a loss loomed, it projected its own fears onto voters in the hope of scaring them into voting Liberal.

Many voters, warned that not voting Liberal will lead to instability, must have felt they were experiencing a new level of political satire.

And in claiming underdog status yesterday, it was astonishing that Morrison conceded that Sharma was likely to lose. Politicians are experts at denying the obvious in the name of faith and self-belief, so the PM's admission looked like the Liberals were already raising a white flag.

Labor candidate Tim Murray - most likely finishing with the bronze in the by-election, an outcome necessary for Phelps to win (if she's in third place, it's unlikely her preferences will flow to him) - said during the campaign that the seat was the Liberal's to lose.

And boy did they accept the challenge.

It's would be difficult for the Coalition to have planned a worse last week of the campaign to parade before already annoyed voters ahead of today's ballot.

ANU's Professor John Hewson, 25 years ago the former Liberal opposition leader and Wentworth MP, said the PM was "all over the shop" hunting for policies that resonated.

“In the last week or so, out of fear of losing the Wentworth by-election, necessitated by the sudden exit of Turnbull, our immediately ex-PM, Morrison has been all over the shop attempting to consolidate populist sentiment among various constituent groups in Wentworth," he said.

“For example, on whether religious schools should be able to discriminate against gay and lesbian students, or teachers, he has held positions ranging from, it’s OK because they already have that power, to yes we will legislate against such a power, at least as far as students are concerned. Whatever answer was required in the circumstances of the day. But, certainly, not unrelated to the fact that Wentworth has the largest LGTBI community of any electorate.”

On top of that, Monday brought the "It's ok to be white" debacle in the Senate, where the government sided with Pauline Hanson's motion, which was nonetheless defeated. Senior ministers then issued a series of embarrassing mea culpas and called for the vote to be retaken so they could vote against it and defeat it again.

Then Scott Morrison floated the idea of following in Donald Trump's footsteps and moving Australia's Israeli embassy to Jerusalem - Wentworth as a high proportion (12.5%) of Jewish voters - but the folly of that idea was soon revealed in a damaging leak of ASIO documents warning of the dangers. Adding to Morrison's woes, Indonesia, the world's most populous Muslim nation, bristled at the idea and a trade deal with Australia suddenly appeared in jeopardy.

Add environment minister Melissa Price reportedly insulting a respected former Pacific Islands leader, denying it "100%" in Parliament then saying she can't recall, plus leadership speculation in the Coalition's junior partner, The Nationals, with Barnaby Joyce keen to retake his old job, and the government looked shambolic and self-absorbed.

It's the small details too. As the AFR's Philip Coorey recounted this week, the loss of female MPs who are stepping down at the next election meant that when Morrison appeared at the Despatch Box during question time when Parliament returned on Monday, it was a wall of blokes behind him nodding at the PM's every word.

As Coorey says: "No one stopped to think that the imagery of the Prime Minister in question time with an all-male cast behind him might not be helpful."

Losing Wentworth won't be fatal for Morrison's team - it's just more wood on the growing bonfire of embarrassments the government has built itself.

But it will send even more terror through Coalition ranks as a general election looms by mid-2019.

Setting up for victory and a third term next year was supposedly one of the reasons Turnbull was rolled.

But if today's vote goes against the Liberals, then just as Labor was demolished in 2013 after years of leadership instability, despite a generally successful economy, the Coalition must be feeling a strong sense of both deja vu and karma coming for them.

Losing Wentworth - and thus ending the Coalition's one-seat majority in the lower house - won't bring down the government. There are three sitting weeks until the summer recess, then 2019 will flick the switch to campaign mode.

But losing the jewel in the Liberal crown for the first time in history because of a leadership spill the government still can't explain will surely be a sign that the Coalition is going down.

Attention in the government ranks will then turn to how many souls the election will take with it.

The sight of MPs fighting for their own lives won't be pretty. And you can guarantee that the policy decisions they make in that climate won't be good for the country.

It's a reminder of the cost when you back the wrong horse.

UPDATE: As polling got underway today, Sportsbet said 49% of money wagered is now on Phelps, who's shortened to $1.32, while Sharma is now drifted to $3.20 from $3 yesterday.