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TORONTO -- Quebec’s ban on religious symbols is a “lifeline” for the Bloc Quebecois and a “hell of a problem” for the federal Liberals in the upcoming election, according to noted election watchers.

Pollster Nik Nanos said it’s imperative for the Liberals to pick up seats in Quebec that are currently held by the NDP and used to be Bloc strongholds. The Bloc will also be vying hard for those seats, setting up an interesting showdown over secularism and Quebec sovereignty.

“These are rural Quebec seats where nationalist sentiment runs strong, where support for the ban is strong and I'm not sure the Liberals can effectively square the circle on being opposed to the ban, and then asking those very same voters to support the Liberals,” said Nanos on the latest Trend Line podcast.

Nanos says it could be a “stink bomb” issue for the Liberals and he expects the Bloc will bombard voters with warnings that Trudeau will lie low on Bill 21 during the election, but will mount a court challenge if the Liberals get back in power.

“This Bill 21 and the religious symbols is a lifeline to the Bloc Quebecois. It gives them something to talk about. It allows them to attack Ottawa.”

The Bloc can go after both the Liberals and the NDP, says Nanos, because the NDP is firmly against the ban. Leader Jagmeet Singh, who wears a turban himself, called it “state-sanctioned discrimination” on day one of the election campaign.

Bill 21 prohibits people in positions of public authority from wearing religious symbols while at work. It would prevent a teacher, police officer or judge from wearing a hijab or turban, for example. Provincial legislators say it ensures religious neutrality and secularism in the public service.

The National Council of Canadian Muslims and the Canadian Civil Liberties Association have filed a legal challenge, arguing the bill is unconstitutional.

“I’m totally against Bill 21. I don’t think that in a free society we shouldn’t legitimize or allow discrimination against anyone,” Trudeau said Wednesday as he kicked off Liberal election campaign.

He said the court challenge shows the system is working as it should and that it would be “counterproductive” for Ottawa to intervene in a provincial debate.

At a campaign announcement in Quebec on Friday, however, Trudeau did not rule out a federal challenge.

“I will highlight that we're not going to close the door on intervening at a later date because I think it would be irresponsible for a federal government to close the door to intervention ever on a matter that does touch fundamental freedoms.”

Former Bloc Quebecois leader Gilles Duceppe told CTV’s Power Play Thursday that Bill 21 poses a huge dilemma for Trudeau. If he says he will defend religious freedom, he will lose support in Quebec. But if he vows not to intervene, it could be a problem with the rest of Canada.

“It’s a good card for the Bloc,” says Duceppe.

Nanos goes much further, saying the religious symbols ban is bringing the Bloc back from the dead.

“I guess if you're a federalist it's kind of like that bad movie where you think the monster's dead and they come back to life,” he said. “For the Bloc Quebecois, what we know from a polling perspective is that usually onto themselves it's hard for them to move the numbers. They're very good at reacting to events.”

So if there is anti-French Canadian sentiment or negative things said about French language rights or a perception that Quebec “is not getting its fair share in the federation,” voters in Quebec then tend to support the Bloc, not out of ideology, but on a strategic nationalist or emotional basis.

“They vote for the Bloc in order to send a message to English Canada that they don't want English Canadians meddling in the affairs and society in the province of Quebec.”

Conservative Leader Andrew Scheer has said a Conservative government will not intervene in Bill 21, but that a federal government under his leadership would not enact similar legislation.

Scheer has set his sights on gaining ground in Quebec, even opening his official campaign in Trois-Rivieres, a riding not held by a Conservative in decades. He vowed to surprise people by winning seats “all over Quebec.”

Quebec is a key battleground for the NDP, which mounted a surge there in the last election, taking 14 seats and edging past the Conservatives’ 11 and the Bloc’s 10.

Nanos says Singh’s approach to talking about Bill 21 is “clever.” Singh highlighted how he stands out as a candidate, just as Quebec is different from the rest of Canada. He added that Singh will hope to connect with Quebec voters in the way the late NDP leader Jack Layton did, with charisma and personality.