For NDP Leader Tom Mulcair, Friday’s French-language debate is seen by many as his final shot at knocking down his opponents and winning back votes in the make-or-break ridings of Quebec.

The province helped give the NDP its Official Opposition status back in 2011 as Jack Layton’s “Orange Wave” swept the region, but recent polling seems to show a change in the tide.

A recent Nanos poll published Thursday suggested support for the New Democrats has softened since the first French-language debate.

“Things are very fluid indeed,” Antonia Maioni, a political science professor at McGill University, told CTV’s Power Play on Thursday. “If the NDP continues to slide, it’s going to bleed not only support but also seats to the Conservatives in Quebec City and the Liberals in and around Montreal.”

Many have pointed to Muclair’s recent comments on the niqab to explain the shift in polls. Mulcair said he supports women who choose to wear a niqab at Canadian citizenship ceremonies, an opinion that counters the overarching sentiment in Quebec.

But Maioni says the niqab debate isn’t the full story.

“There has to be more to it than that,” she said. “On the niqab issue, it’s a larger issue at stake -- it’s the question of values.”

Maioni says anti-Harper sentiment is still alive and well in Quebec, and the province hasn’t totally “warmed” to the idea of Liberals in office. But now the NDP -- once seen as a “vehicle for change” -- may appear to some voters to not share the province’s beliefs, she said.

“The NDP has shown that perhaps it doesn’t reflect all of the values that Francophone Quebecers have at heart,” she said.

If the slide continues, Muclair’s campaign will “essentially be out of business,” CTV's Chief Political Commentator Craig Oliver said of the NDP leader.

"It's always a problem when you've got too many eggs in one basket, and his are all essentially in Montreal," he said.

If Mulcair has any hope of wooing back Quebec`s support, it’s through an emotional appeal, Maioni says.

“He’s talked to Quebecers about his platform, they’ve seen it,” she said. “He has to speak to their values, to their passions, he has to speak to the fact that if they want change in Ottawa, the NDP party is going to do that. He has to convince Quebecers of that fact.”

The three main leaders were in Quebec Thursday on the eve of the debate.

Mulcair and Liberal Leader Justin Trudeau appeared at campaign events, while Conservative Leader Stephen Harper stayed out of the political spotlight.

When asked why his party has not appeared to benefit from the NDP’s decline, Trudeau said he has been pleased by the response to Liberal candidates campaigning across the country.

The Liberal leader, who pledged Thursday morning to spend $20 billion for transit projects over the next decade, said his party is committed to investing in Canadians, including Quebec residents. Trudeau said that, if elected, his party would help fund a light-rail line on Montreal's Champlain Bridge and a rapid transit project on the West Island.

"Quebecers are, like many Canadians, worried about their future," he said. "They need a political party that is willing to form a government that invests in them, and gives them that direct support."

Meanwhile, Mulcair said an NDP government would spend $200 million over four years to help retrofit homes and apartments across the country to help make them more energy efficient. The NDP leader said the country needs a new leader who has a long-term vision to fight climate change.

Oliver said while all of the party leaders will be looking to win seats in Quebec, the Liberals may have the most to gain if Mulcair continues to "leak support."

"If Mr. Mulcair is leaking support and on a downward spiral that we're beginning to see, it's hard to believe those votes are going to go to Harper," he said.

Conservative Leader Stephen Harper had no public appearances scheduled for Thursday, the day after he made a speech in Quebec City, where he laid out his party’s main priorities.