Justin Trudeau's three main political rivals attacked his record in office with impunity Thursday after the Liberal leader was a no-show for the Maclean's/Citytv debate — leaving viewers with the impression that the last four years have been anything but positive.

While he finished the day on a high note with an amped-up, high-energy rally in Edmonton, his opponents had free rein in front of a television audience.

At times the debate was a sort of "greatest hit" list of the prime minister's perceived failings in his first term: the SNC-Lavalin debacle, unbalanced budgets, a major pipeline purchase, troubled Crown-Indigenous relations, a fractious relationship with China and a much-mocked trip to India.

A relatively subdued Conservative Leader Andrew Scheer dismissed Trudeau as an unethical and wasteful spendthrift who has run up budget deficits.

NDP Leader Jagmeet Singh, who was punchy, and well-prepared in his attacks, branded Trudeau as a callous leader who uses "pretty words" while also mocking First Nations people living in Grassy Narrows with a poisoned water supply.

Singh pointed to the ready access SNC lobbyists had to the prime minister's office as proof Trudeau isn't in it for average Canadians. "Mr. Trudeau hasn't shown up for people for four years and he hasn't shown up today for the people," Singh said.

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NDP Leader Jagmeet Singh said Prime Minister Justin Trudeau has fallen short on promises to families, but said a Conservative government under Andrew Scheer would be worse. 0:24

Green Party Leader Elizabeth May, an experienced debater after 13 years at the helm of her party, piled on, calling Trudeau a half-hearted climate fighter who's irresponsibly accepted the former Conservative government's emissions reduction targets in the face of a climate "crisis." She chided the Liberal leader for his "massive betrayal" on electoral reform.

"I think I've found some consensus. I think we can all agree Justin Trudeau is afraid of his record," Scheer said early in the debate.

"We can all agree on that. We can now sing Kumbaya and keep going," May said in support.

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And kept going they did, unloading on Trudeau's record for the better part of two hours. Trudeau, meanwhile, was at an Edmonton rally where he couldn't respond to the many reputational slights.

Trudeau refused an invitation to this televised exchange, saying he'd only commit to the two debates organized by the debates commission and another one in French on the widely watched Quebec network TVA.

There isn't a rich tradition in this country of leaders' debates taking place without the sitting prime minister, let alone with an empty podium on stage to remind voters of a leader's absence, but that's what organizers of the debate did Thursday.

British network ITV gave former prime minister Theresa May the "empty chair" treatment in 2017 when she declined an invitation to participate in a debate. Current British Prime Minister Boris Johnson faced similar treatment by another network, Channel 4, this summer during the Conservative leadership race.

Despite some pointed attacks designed to paint him as sort of Doug Ford "lite," Scheer proved reluctant to engage with his two progressive opponents.

A Conservative majority government depends on a strong showing from the NDP and Green parties on Oct. 21 and a divided centre-left vote.

Watch: Scheer refuses to rule out appealing decision that awarded billions to Indigenous children

Conservative Leader Andrew Scheer came under attack for refusing to rule out appealing a Canadian Human Rights Tribunal ruling that awarded billions to Indigenous children. 0:51

When attacked by Singh on pharmacare and by May on the environment, Scheer pivoted to what he called Trudeau's failings on the same issues.

"Justin Trudeau is trying to do to Canada what Kathleen Wynne and the Liberals did to Ontario," he said at one point when pressed on what sort of cuts a Conservative government would make to balance the books.

Even when accused of cozying up with the Yellow Vest movement, which includes some blatantly racist and white nationalist elements, Scheer kept calm. "Try to stick to the facts," Scheer said to Singh on that charge.

'None of what Mr. Singh just said is true'

Beyond attacking Trudeau, Singh and May traded barbs throughout the night as they both look to bring disaffected Liberal voters into their respective parties.

May questioned Singh's math on a costly plan to dramatically expand a proposed national pharmacare program to include things like dental care, mental health and hearing aids. She said public dental care would cost federal coffers $38 billion and Singh's pledge to close tax loopholes and target offshore tax havens simply wouldn't produce the kind of money he needs.

NDP Leader Jagmeet Singh is trying to highlight how his party is different from both the Liberals and the Greens. (Frank Gunn/The Canadian Press)

She swatted away what she called a "ludicrous" suggestion from Singh that the Greens would prop up a Conservative minority government.

Singh, meanwhile, mocked May's suggestion that SNC-Lavalin should go to work building infrastructure projects on First Nations reserves. "Why can't you just accept it — it was a bad idea," Singh said.

Watch: Singh and May spar over infrastructure projects on First Nations reserves

NDP Leader Jagmeet Singh called Green Party Leader Elizabeth May's suggestion that SNC-Lavalin should go to work building infrastructure projects on First Nations reserves 'ridiculous.' 1:05

"I am not going to go down the little rabbit hole that Mr. Singh created. People can check — none of what Mr. Singh just said is true," May said.

The two parties have been locked in a battle for progressive voters not just at the federal level but also in provincial races where Greens have eaten into the NDP's share of the left-wing vote in places like Atlantic Canada and in British Columbia.

The dynamic has soured even more in recent days after some New Brunswick NDP candidates jumped to the Greens en masse.

The NDP has struggled to distinguish itself in an era when the country is led by arguably the most progressive prime minister the country has seen since former Liberal prime minister Pierre Trudeau or Lester B. Pearson before him.

Justin Trudeau has implemented the generous Canada Child Benefit program and hiked taxes on the wealthy, all while promising further reforms like a national pharmacare plan and ambitious investments in the nation's housing stock, two policies long part of the NDP playbook.

Elizabeth May, leader of the Greens, was the most experienced debater of the three candidates on stage. (Frank Gunn/The Canadian Press)

In his closing remarks, Singh promised to go further and deeper than the Liberals. "We don't fight for the powerful and the wealthy. We will fight for you."

The Green Party, meanwhile, has seen a steady increase in its polling fortunes since the Liberal government announced it would purchase the Trans Mountain pipeline expansion from its U.S. parent, Kinder Morgan.

May has also sought to frame herself as an ethical alternative for voters frustrated by politics as usual.

"The time for status quo decision-making is over. The time for status quo, short-term politics where every party goes out to beat their own drum and kick the others in the shin is over," she said.

Scheer just looked ready for the next debate, when he can take on the man he clearly sees as his only worthy opponent: Trudeau.