This was a particularly interesting week for Steven Guilbeault — one of Canada's most prominent environmentalists — to announce that he hopes to be a candidate for the Liberal Party in this fall's general election.

It would be a notable development regardless of its timing: the recruitment of a star candidate by a government seeking re-election, for a Montreal riding that the Liberals hope to pick up from the NDP.

But Guilbeault's Friday announcement came just three days after the Liberal government re-approved the Trans Mountain expansion.

And Guilbeault is not a fan of pipelines.

That could make for an awkward fit. But the Liberals might be happy with the awkwardness.

Three years ago, Guilbeault was invited to address a Liberal Party convention in Winnipeg. He spoke for 20 minutes and largely praised the new government's efforts. But then, near the 16-minute mark, he pivoted.

'I know this is hard for some of you to hear'

Addressing Trudeau directly, he reminded the prime minister that, as Liberal leader, he had said that governments issue permits but communities give permission.

"Prime minister, large pipeline projects have failed to gain social licence from all across the continent, from Lincoln, Nebraska to Kitmat, B.C., to Montreal, Quebec. Communities don't want them," he said.

"The atmosphere and our climate certainly don't need them. And many of us believe we cannot build pipelines and meet our international climate commitments at the same time. And with a world working around the clock to avoid the worst effects of climate change, it makes no sense from an ethical and a moral perspective to produce and ship more of a substance that is causing a problem that disrupts the future of our children and grandchildren."

Anti-pipeline protesters gather outside the Liberal government's cabinet retreat in Nanaimo in August, 2018. (Benoit Roussel/CBC)

This was two years before the Trudeau government would actually own a pipeline. But Trudeau had said already that getting Canada's resources to new markets was one of the chief responsibilities of the federal government.

"I know this is hard for some of you to hear," Gilbeault said, "but I believe it to be the truth and I'm not the only one."

Guilbeault now notes that it's not entirely clear the Trans Mountain expansion will lead to an increase in Canada's emissions. Much will depend on whether the pipeline is used to transport oil that otherwise would have travelled by rail, or whether it leads to an increase in production. It could require Canada to "work harder" to reduce its emissions, he said.

The enemy of my enemy ...

Either way, he still believes Canada shouldn't be investing in new infrastructure for fossil fuels.

So why is he running for the Liberals?

"I disagree with the pipeline," he told CBC News. "But when I look at everything that the Liberal government has done over the past four years, in terms of fighting climate change ... there's so much for me to rally around that, despite this point of disagreement, I've decided to go ahead."

But wouldn't he be more at home with the NDP or Greens, two parties which also oppose the Trans Mountain expansion?

"I do fear that the Conservatives could win the next election and, if they do, everything we've worked for in those past four years will be gone and we will be back to what was happening under the Harper years," he said. "The only party that can stop the Conservatives ... is the Liberal Party of Canada."

This, one imagines, is exactly what the Liberal Party will be saying to progressive swing voters this fall.

'It's complex'

Guilbeault said Trudeau "has no issues with me saying publicly that I disagree with the pipeline." But Guilbeault also said he is willing to be pragmatic in the pursuit of better environmental policy; he stood on stage beside Premier Rachel Notley in November 2015 when she announced a new climate agenda for Alberta.

"I think they did it because they wanted to help Alberta," Guilbeault said of the Trudeau government's decision on the Trans Mountain expansion. "And I understand. I can see why they did it. I can see what's happening in the province. Economically, it's been very difficult. Oil is still 25 per cent of the economy there. And the transition we're going through, it's not easy.

"And for people to claim that they have the answer, well, I'm sorry, but I've been working on this for 25 years and I've been going all around the world and I've been looking at what governments all around the world are doing, and I don't think anyone could raise their hand and say, 'Hey, we have it, we've found the way to transition.' It's complex."

The Greens and New Democrats might disagree — or at least insist that Trudeau's approach definitely isn't the correct one. (Elizabeth May said she was "shocked" by Guilbeault's decision to run for the Liberals.) Guilbeault said that, fundamentally, the Liberals, New Democrats and Greens are not far apart on climate change, apart from two differences. First, that pipeline. Second, "that one of these parties has had to govern a country for the last four years."

It's not inconceivable that Guilbeault's candidacy could be problematic for the Liberals. Jason Kenney or Andrew Scheer might try to use his presence on the ballot to bolster their argument that Trudeau is biased against the fossil fuel sector. But the voters most likely to agree with that criticism probably weren't going to vote for the Liberals this fall anyway.

When Trudeau announced the re-approval of the Trans Mountain expansion this week, he spent a considerable amount of time trying to justify the decision for those with environmental concerns.

"I know some people are disappointed by this decision," he said.

Those disappointed voters are the ones that Trudeau wants to reassure and rally over the next four months. They're the ones who might care that Steven Guilbeault is still willing to run for the Liberals. And they're the ones who will be reminded that (unless the polls swing dramatically), the likeliest alternative to a Liberal government is a Conservative government.

To some extent, Justin Trudeau might need someone like Guilbeault at a moment like this. Which means that Guilbault might end up with a significant amount of political capital if he ends up sitting on the government benches after this October.

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