Tom Mulcair is spending two days in the province that vaulted his party to the offices of the Official Opposition but polls suggest the NDP's dominance in Quebec has weakened and, with just three days to go before the election, his ability to approximate the success of 2011 is very much uncertain.

Party strategists point out that most of the 59 New Democrats who were elected here four years ago – under a different leader with a different personal cachet – won by wide margins. It stands to reason, they argue, that a drop in support by 10 or even 20 percentage points still adds up to a large number of wins. But it could also result in a devastating loss.

Mr. Mulcair and his party saw their numbers start to drop across the country, and in Quebec in particular, about three weeks ago when he defended a woman's right to wear a niqab while swearing her citizenship to Canada. NDP incumbents are now fending off tough challenges from the Bloc Québécois, the Conservatives and, more recently, the Liberals. The surge in popularity of Justin Trudeau has moved seats that were safe for the NDP two months ago into the category of too close to call.

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Mr. Mulcair is responding by visiting ridings held by Conservative cabinet ministers, acting like the aggressor rather than someone who is just trying to hold together the fort. On Friday, he will visit Mégantic-L'Érable, where Christian Paradis, the International Development Minister, isn't running again. And on Thursday, he was in Alma, where Infrastructure Minister Denis Lebel holds the riding of Lac-Saint-Jean. The only way to beat Stephen Harper on Monday is to win Conservative ridings, Mr. Mulcair told a small room of supporters in Alma. "And I am working very hard to defeat Conservatives because I know Canadians and Quebeckers deserve better."

But he can feel the hot breath of the Liberals on his neck. And Mr. Trudeau spent part of Thursday campaigning in Mr. Mulcair's own Montreal riding of Outremont.

"It's a free country," Mr. Mulcair replied when asked about the Liberal Leader's venture into his turf. "People are allowed to do as they will during an election campaign. But I will say this to you: My adversary in this election campaign is Stephen Harper. He's the person I have to defeat and replace to get Canada on track."

The most recent public opinion survey by Nanos Research suggests the NDP and the Liberals are in a dead heat in Quebec. But Nik Nanos, the president of the polling firm, said he is not yet writing off a strong finish for the New Democrats in this province.

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"There is still time for the numbers to move," Mr. Nanos said Thursday. "Things happen in the last two to three days of the campaign because people are in the zone where they are focusing on firming up their vote decision."

Even if one out of every 20 Quebeckers changed their views between now and Monday, that would create a five-point swing and that could change the complexion in a number of seats, he said. "Mulcair needs to jump-start the Quebec numbers and he needs a wedge against the Liberals," Mr. Nanos said.

The New Democrats were given a gift Wednesday, he said, when Daniel Gagnier, an energy industry consultant who was also the co-chair of Mr. Trudeau's campaign, resigned after it was revealed he sent a note to TransCanada Corp. officials to tell them to target the right people in government as soon as possible regarding the company's Energy East pipeline. Mr. Mulcair said the note from Mr. Gagnier reminds Quebeckers it was Liberals who were behind the sponsorship scandal that saw them turfed from power in 2006. "They're being reminded again that it really is still the same old Liberal party. They can put a fresh face on it. But behind the scenes it's still the same old gang pulling the same old tricks," said Mr. Mulcair.

Mr. Trudeau, he said, has been saying that the pipeline's approval would depend on it obtaining a social licence. But "he's already given the Liberal licence. There's not going to be any debate or discussion with the public about this. It was going to go through. That's the truth that has come out with just a few days left in this campaign. You can't trust the Liberals."

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When he departs Quebec on Friday for the last time before returning to learn the results of the election, Mr. Mulcair knows he has given Quebeckers who were considering switching from NDP to Liberal something to think about. The question is, is it enough?

Antonia Maioni, a professor of political science at McGill University in Montreal, says this election represents the first true test of the unlikely pan-Canadian coalition won by Jack Layton in 2011 that brought together Canadian social-democrats and Quebec nationalists.

"There were bound to be issues that would reveal the tension there," Prof. Maioni said. The most obvious, she said, is Quebec sovereignty. But, "what the niqab issue did was to shine a light on the NDP for Quebeckers who, having given the NDP their protest vote there in 2011, were now giving the NDP the twice-over, and realized perhaps the party was not on their radar in in the context of larger discussions of identity and reasonable accommodation."

The Liberals, on the other hand, said Prof. Maioni, are still not favoured by the francophone voters in Quebec and Mr. Trudeau's personal popularity, is concentrated on the island of Montreal and in classic Liberal strongholds. "The Liberal party is moving back to their pre-2011 position of strength in those ridings," she said, "but has yet to overcome the wider problem of the brand and its leader. We'll see on October 19th."

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