OTTAWA - The political weight attached to whether and where to build pipelines in Canada came through clearly Thursday night in the French-language leaders' debate, in a spirited two-hour contest that marks a milestone for the federal election campaign.

Advance polls open Friday and with them, the countdown to the Oct. 21 election day begins in earnest.

The six federal party leaders argued over a wide range of subjects that had yet to be tackled in detail so far in the campaign, including digital rights and Canada's trade with China.

But it was pipelines that kept coming up, so often that moderator Patrice Roy, a Radio-Canada host, even chided the leaders for bringing them up in a segment that was supposed to be about immigration.

The politics of building them loom large in Quebec, along with the battle against climate change, and all six leaders on stage Thursday were to some degree fighting for their political lives in a province whose voters can decide whether a party wins a majority government.

NDP Leader Jagmeet Singh and Green party Leader Elizabeth May used Liberal Leader Justin Trudeau's decision to nationalize the Trans Mountain pipeline as a cudgel to repeatedly whack down any further pledges his party might make on the environment. Bloc Quebecois Leader Yves Blanchet used it also as a proxy - how could the Liberals afford that, but not money for Indigenous children, he wondered.

Those three, plus Conservative Leader Andrew Scheer and People's Party Leader Maxime Bernier, did repeatedly gang up on Trudeau, though he was most often placed on the defensive by Scheer, who rarely missed a chance to pivot an answer into an attack on the Liberal's record.

The duo repeatedly accused each other of being ridiculous or engaging in half-truths, including on the costings of their respective platforms. The Liberals have not included the price tags for significant elements of theirs, while the Conservatives' full costing is expected to only be made public on Friday.

But Blanchet often found himself in the crossfire as well; polls suggest his party is surging in support in Quebec and the other five leaders he shared a stage with on Thursday are losing support as a result.

Scheer tried to paint Blanchet as a separatist, accusing him of “hiding his true intentions,” while Trudeau suggested Blanchet's plan for the environment wouldn't work without a federal government that had national support to implement it.

Singh, who earlier in the day had dismissed Blanchet's rise in support, sought to taint him as just being pro-pipeline, and in that way no different from Scheer.

Scheer's conservatism was also attacked from the other direction by Bernier, who attempted to paint his former Conservative party colleague as simply another version of the Liberals. Positioning his own party as far more conservative than the one he left has been a key strategy for Bernier.

“Mr. Trudeau and Mr. Scheer have the same stance on climate change,” he alleged, before further attacking one pillar of Scheer's approach to address emissions abroad.

Trudeau sought to cast Scheer and Bernier as the climate-change outliers, saying there were only “four of us here who will fight to protect the environment.”

May was making her French-language debate debut in the current campaign. The previous French debate, hosted by television network TVA, excluded her, though she followed along on social media.

May said another hot-button issue in Quebec, a bill that forbids the wearing of symbols of faith by some of the province's public servants, should not be as much of a debate during this campaign as it has.

“We have talked more about that than the climate crisis, and that worries me.”

She stressed her party's credentials, returning to her familiar refrain that climate change needs more urgent action because “our house is on fire.” And she echoed Swedish climate activist Greta Thunberg early, saying the other leaders don't take the issue seriously enough - “How dare you?” she demanded.

But she faced grilling over how she'd pay for her climate plans.

Thursday night's French debate got off to a much less frantic start than the officially sanctioned English debate on Monday, also at the Canadian Museum of History in Gatineau, Que.

Monday's two-hour contest in English included lengthy bouts of crosstalk and mudslinging and several leaders had complained the format didn't allow enough time to get their points across.

Still, voter surveys suggested the two previous televised debates gave a boost to the NDP and Bloc Quebecois, but didn't move the needle for the front-running Liberals and Conservatives.

The NDP's continued loss of support in a province that once handed them official Opposition status is a continued sore point for Singh. Earlier Thursday he had shrugged off the fact the Bloc Quebecois is picking up some of those voters but went after the Bloc's environment stance Thursday night.

Meanwhile, Scheer was widely considered to have taken the hardest hit in Quebec after the previous French-language debate, and though his aides had been bullish on Tory chances in the province, they've now dialled back that enthusiasm.

Thursday's debate featured five themes: economy and finances, environment and energy, foreign policy and immigration, identity ethics and governance and services to citizens.

This report by the Canadian Press was first published on Oct. 10, 2019.