Remember that large sinkhole that appeared this week in Point Piper, the suburb of Malcolm Turnbull’s harbourside mansion?

The gaping ground presented particular difficulties for local authorities. Contractors and investigators arrived, but it couldn’t be quickly filled in because the cause remained unclear. So as an interim measure it was lined with black plastic.

The hole became an obvious metaphor for Turnbull’s situation. The year has started with the government staring at an abyss, far from sure it can avoid being swallowed into it. In this first parliamentary week, some plastic has been rolled out but permanent repair looms as a complex task.

Coalition MPs left Canberra after riding a rollercoaster of political emotions.

On Tuesday senator Cory Bernardi had depressed and angered colleagues by walking away from the Liberals to form his own conservative party. But a day later the troops’ spirits soared at the spectacle of “mongrel Malcolm” savaging Bill Shorten as a “hypocrite”, a “parasite”, and a “social-climbing sycophant”, with knees under billionaires’ tables, sipping Cristal.

This has been dubbed by Labor as the “know-your-place speech”. (Shadow Treasurer Chris Bowen apparently doesn’t have to be told his place – he had to ask Tanya Plibersek what Cristal was.)

“It’s amazing how ten minutes can change the whole morale of the team,” said one Liberal MP, although there are varying opinions on how it will go down among ordinary voters, who mostly hate the gutter wrestling of politics. Another Liberal member said Turnbull had needed “to fire up the base”.

By week’s end, partly because of their better mood, even the Bernardi defection had come to seem less significant than it had initially appeared to many Liberals.

On Thursday Turnbull returned to his personal attack on Shorten, this time outside the House of Representatives. “He wants to play the politics of envy but yet he’s been a sycophant to the billionaires of Melbourne for years and years,” he told reporters.

He went on: “Politics is about many issues. It is about policies, it is about character, it is about strength of character.”

And to pre-empt the obvious question of his own dealings with billionaires: “I back myself. I am my own man. I can’t be bought by anyone. I don’t suck up to billionaires. I look them in the eye and when I need to I take them on.”

Years ago the “character” of then Labor leader Mark Latham came under intense scrutiny, to his disadvantage. To have one’s character blackened can be lethal for a leader.

The government has prodded and probed around “character” in relation to Shorten but so far without much damage to him.

It thought its big chance was when he was appearing before the trade union royal commission. There were issues about deals done by his Australian Workers’ Union, and his long-term non-disclosure of a big donation when he was running for parliament. But little stuck politically.

At the election, Turnbull resisted running a tough negative campaign focusing on Shorten. When the result was so close, he came under fire from some Liberals for failing to do so. They were unconvinced by the argument that the research had shown people wanted positives. Perhaps it was an opportunity permanently missed.

That Shorten has had an element of teflon about him is deeply frustrating to the government.

Shorten himself is said to have been taken aback and somewhat rattled by the ferocity of Turnbull’s Wednesday attack. He knows as well as anyone that he has critics within Labor who would privately agree with more than a little of Turnbull’s critique, and that Anthony Albanese remains an ambitious alternative if things were to go bad for him.

The leadership of neither Turnbull nor Shorten is currently under threat, but given recent history each has a keen eye to his own back.

One major difference in their respective situations is that Shorten’s internal critics are publicly silent, while Turnbull’s enemies, most notably Tony Abbott, are out in the media all the time.

Labor is not having public arguments among its own about policy. Turnbull is challenged on a regular basis, just a few days ago by reported pressure from moderates over same-sex marriage. With a one-seat majority, he’s periodically subjected to threats from the Nationals’ George Christensen, who this week tweeted he would support Bob Katter’s bill for a commission of inquiry into banks.

And now in the media there is speculation about his leadership, though the form guides just underline the inadequacies of the alternatives.

Apart from denigrating his opponent, Turnbull this week was trying to deal with his “sinkhole” by projecting two messages: that the government understands and wants to help with the cost-of-living pressures faced by families, and that it has heard and taken on board the public’s disgust about politicians having their noses in the taxpayer trough. But neither message can cut through effectively with the constant distractions and noise.

Legislation was brought forward to reform child care, to the benefit of lower- and middle-income families. And Turnbull and ministers continued to strongly push energy security, again highlighted by the latest blackout in South Australia.

But the political pluses of the childcare changes compete with the political negatives of savings being extracted from family tax benefits; anyway, Turnbull chose to drown out the child care policy with his blast at Shorten. The energy message suffers from the Coaliton’s lack of a clear, comprehensive and convincing policy of its own.

The government is again tackling politicians’ entitlements – which Turnbull wants to call “work expenses” – but the problem is that a cynical public is likely to just go “Oh yeah?” The political damage from revelations of abuse is always greater than the credit received for any remedial action.

When Liberal MPs come down from the “high” of watching their leader’s roasting of Shorten, they will be back to looking at the polls, and whether they show any sign of improving. This week Newspoll had the Coalition trailing Labor 46-54%; in Essential it was 47-53%. Turnbull made bad polling numbers central in spearing Abbott. Now they are becoming a weapon against him.