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Thomas Mulcair's deliberate move to the centre of the policy spectrum has disillusioned some long-time, left-leaning elements within his party. But the prospect of an NDP government in Ottawa – one that will represent the voice of the Canadian labour movement – is preventing dissenters from abandoning ship.

Perhaps the most telling indication of the New Democratic Party's willingness to step back from its socialist ideals was the removal from its website of the 29-page book of policies passed by New Democrats at party conventions over the years.

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Barry Weisleder, a founder of the NDP socialist caucus, said in a telephone interview on Sunday that the book's disappearance "is indicative of, not only the lurch to the right, which has been going on for decades in the party, but the strangulation of internal democracy."

The members of the socialist caucus are circulating a petition praising Mr. Mulcair for his efforts to bring in a national minimum wage and a national childcare plan, but demanding that much more from the traditional NDP playbook be incorporated into the party platform. They want national pharmacare, a ban on pipeline creation, more "progressive taxation" and solidarity with Palestinians over Israel.

As it stands, some of the policies being unveiled by Mr. Mulcair seem more centrist than those proffered by Justin Trudeau's Liberals.

It is Mr. Mulcair, and not Mr. Trudeau, for instance, who is promising he will not run a deficit. That may appeal to soft Liberal voters whose support the NDP Leader needs for an election-day win. But it jars those within his own ranks who are more concerned with issues such as income redistribution than turning government books from red to black.

Mr. Mulcair will tell Canadians this week how he plans to meet his policy commitments without running a deficit.

The NDP Leader's pledge to balance the budget "come hell or high water" is disturbing, said Mr. Weisleder. "The idea that, without significantly increasing taxes on the corporations and the super rich, he will be able to deliver even the child-care plan seems like a fantasy."

John Orrett, another member of the NDP socialist caucus, agrees. The talk of balanced budgets "is the talk of neo-liberalism and governments that want to oppose austerity," he said. "I don't understand why [Mr. Mulcair] is picking up the language, the paradigms of the right wing." But, despite their differences with the party leadership, both Mr. Weisleder and Mr. Orrett remain fervent New Democrats and are eager to see an NDP government oust Stephen Harper's Conservatives.

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Mr. Orrett said he "absolutely, 100 per cent, unequivocally calls for a vote for the NDP." The New Democrats are still the party of labour, he said, and "until they have totally run their historical mission and totally betrayed who they say they are fighting for, it's still a vehicle."

The bigger question is how Mr. Mulcair's promises will be perceived by voters at large – those who do not have loyalty to the NDP.

Henry Jacek, a political-science professor at McMaster University in Hamilton, said roughly 15 per cent of voters are willing to support the Liberals or the New Democrats, depending on which party is best positioned to get rid of Stephen Harper. Those people want to see the government intervening in the economy to create jobs, and Mr. Mulcair needs their support, he said.

So "I do think he's got a problem here," said Prof. Jacek of Mr. Mulcair. "He's been outflanked in various ways by Trudeau and Trudeau is actually sounding like a Keynesian New Democrat in terms of economic policy. He cannot allow himself to be outflanked by Trudeau."

On the other hand, Mr. Mulcair now presides over a party that is largely based in Quebec where it is seen as a new entity that carries little baggage and where the thought processes that guide voters in other parts of the country don't necessarily apply.

"A large percentage of the population is not ideologically aligned," said Raymond Côté, an NDP candidate in Quebec City who is trying to hold on to the seat that he won in 2011. "They are looking for an option with which they feel confident, and which offers common-sense solutions to the issues that they face."

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James Laxer, a professor at York University in Toronto, who once ran for the leadership of the NDP and is a former research director for the party, said he doesn't believe Mr. Mulcair's centrist tack is a problem for the New Democrats.

"I have never seen NDP voters, or potential NDP voters, as enthusiastic or as hyped about voting NDP as they are now. Never," said Prof. Laxer, a long-time defender of left-wing politics.