According to the report, the Liberal leader went on to say the government and pipeline company TransCanada have failed to demonstrate that they intend to exploit the natural resource in a responsible fashion.

“The project has still not attained the level of support it needs to go forward. I hope they will develop a means to reassure and demonstrate that this can be done in a responsible fashion. But they aren’t there yet, far from it.”

To attain that social licence, Trudeau said the project’s proponents must convince the population that the pipeline is “in the public interest over the long-term.”

Asked whether he hopes for the project’s success, Trudeau responded that it was not up to him to speculate. “It’s my job to observe what’s happening and ensure the level of transparency and scientific and intellectual rigour that people expect.”

This is an unexpected reversal from the Liberal leader, who offered unqualified support for the pipeline project as recently as this fall, and underscores what has been a disastrous few months for the pipeline and its parent company, TransCanada.

According to Trudeau, the Energy East pipeline will be the “major issue” of 2015. Polls now place opposition to Energy East close to 70 per cent in Quebec, and over 50 per cent in the rest of the country, while a whopping 87 per cent of Quebecers think the province should be able to make its own decision on the pipeline. Meanwhile, former student leader Gabriel Nadeau-Dubois upped the ante by raising close to $400,000 for the coalition of community groups opposing the pipeline in the most successful crowdfunder on a political issue in Canadian history.

Quebec and Ontario’s premiers briefly formed a common front, promising to apply their own environmental assessment, which would factor in the effect on climate change of the oil shipped through the pipeline.

However, after a brief round of shuttle diplomacy by Alberta Premier Jim Prentice, both premiers reversed themselves within days, repudiating their own idea of a climate test for the pipeline.

It’s important to note that Trudeau’s position remains slippery. His comments to Le Soleil position him as more hostile to Energy East than the NDP has been to date, but still allow him to pitch himself (in business and right-wing circles) as the prime minister who can help win social license for TransCanada. There’s no clear promise here to kill the project if elected.

For his part, NDP leader Tom Mulcair has attempted to demonstrate that his party does not oppose resource extraction projects, and holds a nuanced view on pipelines. What this has meant in practice is a patchwork policy where his party opposes the Keystone XL pipeline (which the Liberals support) and the Northern Gateway pipeline (which most oppose, because it has little chance of ever being built) while supporting Energy East and taking no position on the contentious Kinder Morgan pipeline in B.C. (It should be noted that NDP MP Kennedy Stewart has taken a strong position against Kinder Morgan, but this is not synonymous with party policy, and the party has refused to take a public position.)

“It’s a win-win to bring it from west to east,” Mulcair told CTV news in November. “It’s better prices for the producers and therefore more royalties for the producing provinces. It’s better energy security for Canada and it’s more jobs here.”

The NDP leader wrote an op-ed in the Toronto Star on Dec. 4, which seemed to temper his previous enthusiasm for the pipeline. In the piece Mulcair argued that the party believed in the need for social licence, and that was the reason for their opposition to Keystone XL and Northern Gateway. The implication seeming to be that while those two projects lacked social licence, Energy East was not so afflicted.

The underlying message of the op-ed was that “New Democrats support increasing west-east capacity,” so long as pipelines are submitted to a thorough review process, and meet a series of criteria. This is in contrast to the new Liberal position that the pipeline has failed to achieve social licence, leading some analysts to suggest that Trudeau had taken a page out of Ontario premier Kathleen Wynne’s playbook, attempting to outflank the NDP to the left.

“This isn’t about ‘good pipelines’ vs ‘bad pipelines,’ because the scientific consensus is clear,” said Cam Fenton, an organizer with 350.org. “To avoid catastrophic climate change we must keep the tar sands oil in the soil. That can’t happen if a single one of these pipeline projects go ahead.”

The shifting discourse from Trudeau is a sign of changing times. Until recently, this pipeline looked like a slam dunk. What a difference three months can make.

The Harper government, of course, has yet to see a tar sands pipeline proposal they wouldn’t support wholeheartedly. Energy East, in particular, is being pitched by Harper and the Conservatives as an exercise in “nation-building” analogous to the Confederation-era railway project. The consensus amongst the three major parties for west-to-east tar sands infrastructure expansion appears to be unraveling. Pundits and politicians of all stripes acknowledge that the pipeline debates will be central to the federal election in 2015.

This flip-flopping from political leaders is indicative of a project which has broad support from the political and business classes, but is overwhelmingly opposed by Canadians, and in particular Quebecers.

As conservative pundit Norman Spector opined on Twitter, “Trudeau backing off support for Energy East (can Mulcair be far behind?)”

It all sets up a fascinating federal election in Quebec next year, where in most ridings the race will be between NDP and Liberals, and the pipeline will be the issue on everyone’s lips.