Let’s start this weekend up north, in Cairns, with a story about the Liberal Warren Entsch and the Greens.

People watching the campaign will know the Coalition has been characterising the Greens as extremists as part of an entirely unsubtle false equivalence exercise to give them political cover for doing preference deals with Clive Palmer and Pauline Hanson.

Entsch, the Liberal incumbent in the north Queensland seat of Leichhardt, either didn’t get the “Greens will never darken our door” memo, or if he did he ignored it, because he’s sending preferences their way.

They haven’t reciprocated, they are putting Labor first, but Entsch, who is said almost universally to be in trouble in this contest, told me this week climate change is such a potent issue in his neck of the woods that it would have been self-defeating for him to do anything other than make the gesture.

In the last election, 20% of Greens preferences came his way, he says, because he is socially progressive – he was one of the leaders of the push to legalise same-sex marriage – and, as he puts it with typical bluntness: “I’m a committed conservationist. I am not a climate change denier.”

Climate change in Entsch’s part of the world is divisive locally because tourism operators are in conflict with anti-fossil fuel activists obsessed with the health of the Great Barrier Reef, but whatever the nuances and conflicts, it’s a front-of-mind preoccupation of his constituents.

The zeitgeist is different in central Queensland, where LNP incumbents believe they are pulling the contest back from Labor in marginal seats by campaigning in support of coal. A feeling of buoyancy has been around since the opening week of the campaign, and it hasn’t shifted, although MPs are nervous about what happens when Labor and the unions turn the money on for the final, brutal, fortnight. But up north, and in the south-east corner, and in the southern states, sensibilities are different.

Let’s continue to follow our breadcrumb trail south. Here’s what happened, minus the noise and distraction of the daily battles: various candidates exploded, Labor and Liberal; contention thundered about Clive Palmer and his preference tie-up with the Liberals; and Bill Shorten decided to go for broke on climate change.

Now let’s thread these things together, because if we do that, we can see the various connections matter.

The Liberal candidates who exploded this week did so in unhelpful locations – Victoria, which is the most vulnerable region in the country for the Liberals, and Tasmania, where the Liberals have eyes on marginal seats in the north.

Victoria is the Coalition’s maximum vulnerability point, because if they lose too many seats in the state to Labor on 18 May – and the risk of that is substantial – that’s it. It’s game over. Bye bye. There is no viable path to victory.

The errant Liberals were bundled out with haste because the views they expressed underscored negative perceptions about the party. The party in Victoria right now does not need their representatives presenting as homophobic, or saying crazy things about Muslims – not in the most progressive state in the country, where voters are already worried that a party of government is vulnerable to takeover by ultra-conservatives and rightwing fringe dwellers.

It’s exactly the wrong message in the wrong place at the wrong time, because it plays to a pre-existing concern at large in the community. And there’s further trouble too, with a revelation far-right ringleader Neil Erikson was one of three extremists who attended a “conservative recruitment event” for the LNP at a private residence on the Gold Coast last year.

Cue the Nationals leader Michael McCormack, who didn’t help by saying breezily mid-week that it was fine for Nationals to do preference deals with One Nation because there was an alignment between the two parties. Not only was that a dumb message for Nationals trying to hold their ground in what looks like a burgeoning bush boilover, it was a deeply dumb message for Melbourne.

Adding to that, we can add controversy about the Palmer tie-up. That preference deal is potentially a lifeline for the Coalition in the parts of Queensland where incumbents are feeling comfortable. It could help the LNP hold their marginals and gain the Labor-held seat of Herbert. That’s why the Liberals held their nose and did it.

But it’s not necessarily a plus elsewhere.

Given the Liberals potentially gain advantage in Queensland courtesy of the deal, Labor has been absolutely determined this week to ensure that whatever is gained in those seats is netted out by problems caused elsewhere. Labor has busted out the foghorns to rail against the Palmer deal in the southern states, casting it as symptomatic of government chaos and dysfunction and abject desperation.

So while Labor was nudging chaos and “you know they are just rightwing crazies who hang out with other rightwing crazies” down the campaign hill, hoping to build a giant snowball to flatten obstacles in its path, Bill Shorten found his voice on climate change, which is the rallying point for progressives in Australia.

The Labor campaign decided this was the week to go for broke on climate change. Possibly it was a coincidence that Shorten found his voice on this at a point in the campaign when the Liberals had suffered a setback in Victoria, and Labor was looking shaky in central Queensland coal country, in part because of the Palmer pincer movement – but I very much doubt it.

It looked like making a choice to build support where your opponents are vulnerable. It looked like getting off the fence.

Shorten also broadened his message beyond the specifics of policy. He said climate change was the ultimate symbol of Australian politics being broken.

Shorten’s pitch was politics is busted and it won’t be fixed until the parliament faces up to the challenge of climate change, and you know Labor will keep taking this issue seriously, and you know the other side can’t, because they’ve been killing themselves over it for a decade.

That bit of narration was the sound of multiple circles being squared: voter concern about climate change – the highest it’s been since 2007; voter disaffection with the state of Australian politics – visceral, and ubiquitous; the most significant negative issue for the Liberals – perceptions that the government is chaotic and hostage to external forces that make the Canberra circus worse and stymie progress.

So after a preamble of several weeks, the 2019 election campaign finally arrived at its focal point.

Shorten, who can’t be presidential because he’s not popular with voters (a message you hear right around the country), has to build an institutional case for changing the government.

He has to make the argument that things can’t remain as they are, and he has to find the right constellation of resonant or salient issues that tell that story, at the time voters are tuning in. Labor is still fine-tuning its formula, but that’s the objective.

Morrison knows it, so he’s doing everything in his power to hammer the costs of making a change. It’s all he can talk about – all the reasons you can’t trust Labor, why it’s risky to change the government.

Morrison needs to keep talking up Shorten’s negatives to try to prevent Labor from gaining momentum as the campaign moves to the business end, but the Liberal leader is beginning to face pressure, for the first time in the contest, about being an empty vessel – a vulnerability that is becoming as obvious as the nose on Morrison’s face.