With polls suggesting he could become prime minister in mere months, Thomas Mulcair has reaffirmed his support for an NDP policy that some critics charge could make it easier to break up the country.
And it appears Liberals are eager to have Mulcair's position discussed on the campaign trail.
At issue is the so-called "Sherbrooke declaration" — the NDP's official policy on Quebec since 2005.
At an event in Quebec City Tuesday, Mulcair made it clear that he sees Quebec sovereignty as something that would harm the middle class and hurt families. The remarks were made one day before Fête Nationale, a holiday celebrating French-Canadian culture.
Yet, Mulcair also reiterated that the Sherbrooke declaration sits firmly "at the heart of (the NDP's) approach with Quebecers." While those remarks are no surprise — Mulcair has long said he is proud of the policy — they made headlines in light of the looming federal election.
The NDP document states that that party would recognize a "majority decision (50 per cent +1) of Quebec people in the event of a referendum on the political status of Quebec."
That position conflicts with the Clarity Act passed by Liberals in 2000 as a response to the Quebec referendum five years earlier.
The Clarity Act, initially supported by the NDP, stipulates that the federal government can only negotiate the terms of a province's independence if a "clear majority" voted yes on a clear referendum question.
While the act does not define what constitutes a "clear majority," the 1998 Supreme Court reference decision that heavily influenced the legislation indicated that the threshold should be higher than a "simple majority."
What Exactly Does The Sherbrooke Declaration Say About Quebec Independence?
New Democrats did not have a single seat in Quebec at the time of the declaration, but clearly saw the battleground province as key to their future.
"If it is to truly and legitimately form the Government of Canada one day, the NDP must have strong support throughout the country. Specifically, that means that the NDP has to make significant inroads in Quebec in the medium and long term," the document states.
"The Quebec question has all too often been a stumbling block for the NDP. However, Quebec must become the cornerstone of a movement aiming to form a government."
The document states the "NDP hopes for and will promote a united Canada," but also recognizes the province's right to self-determination.
"This right can be expressed in various ways and can go as far as achieving sovereignty," it reads.
In addition to vowing to recognize the "majority decision" of 50 per cent plus one, the policy states New Democrats respect the Quebec National Assembly's right to frame a referendum question and have citizens "answer it freely."
"The NDP rejects also any use of — or threat of — force against Quebec at any stage," it states. "Our vision is one of trust toward democracy, good faith and values of peace."
The section ends with a call for a "new attitude towards the whole debate" that positively contributes to the "reinforcement and renewal of federalism."
Trudeau Accuses NDP Leader Of Pandering To Quebec Voters
Liberal Leader Justin Trudeau wasted little time Tuesday blasting Mulcair in an interview with The Canadian Press.
"On the St. Jean Baptiste, Quebec's national holiday, that Mr. Mulcair would decide to make this announcement about repealing the Clarity Act and making it easier to break up the country is just the worst kind of politics," he said.
"The fact that he's choosing to bring this up as an effort to pander to votes in Quebec, I think is exactly the wrong thing."
Trudeau also took to Twitter with a thinly veiled shot at the NDP leader who has also vowed abolish the Senate, a move requiring a constitutional amendment.
Gerald Butts, Trudeau's top adviser, jumped online to accuse Mulcair of pandering to sovereignty. NDP staffer James Smith fired back that Butts was "shrieking about phantom unity issues" because the Liberals have dropped in the polls.
Liberal foreign affairs critic Marc Garneau, who will run again in the Montreal riding of Notre-Dame-de-Grâce-Westmount, said he intends to raise the issue with the NDP candidate in his riding.
And others wondered online if the NDP leader would be willing to defend the Sherbrooke declaration outside of Quebec.
Mulcair Promised To 'Wipe The Floor' With Trudeau On This Issue
The NDP leader has said in the past that he is ready to defend his party's position if comes up during the election debates.
At a speech in Montreal in November 2013, the NDP leader said his was the only party that is actually clear on the issue because, unlike the Liberals' Clarity Act, there's a real number attached to their policy.
According to The Toronto Star, Mulcair told the audience he stands by the threshold and will debate it with "anybody, anytime."
"And I look forward to debating that with Justin Trudeau in 2015, and I know exactly what's going to happen: I'm going to wipe the floor with him," he said.
Trudeau has said on multiple occasions that differences with Mulcair on matters of national unity are among the reasons he doesn't want to form a coalition with the NDP.
"On unity, [Mulcair’s] willingness to break up the country on a 50 per cent plus one vote and repeal the Clarity Act is unacceptable," Trudeau told reporters in February 2014.
In 2011, the NDP won 59 of Quebec's 75 seats en route to becoming the official Opposition. The separatist Bloc Quebecois dropped from 47 seats to just four.
With files from The Canadian Press
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FLASHBACK: The 1995 Quebec Referendum
A copy of the Sherbrooke declaration, uploaded by CBC News: