Outside federal New Democratic Leader Thomas Mulcair's Montreal office, an ex-supporter ripped up her NDP membership card while protesters in blood-stained shirts lay down in a "die-in" to denounce the party's kid-gloves treatment of Israel amid the rising civilian death toll in Gaza.

In Ottawa, another group of disgruntled activists occupied NDP foreign affairs critic Paul Dewar's office to denounce the "dangerous policy shift" that has the party's once-dominant pro-Palestinian faction feeling left out in the cold – and possibly in search of a new political home.

Even the NDP youth wing has weighed in to deplore the "hesitation from our Official Opposition when it comes to standing up for New Democratic values" in the month-long Gaza conflagration.

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If the conflict in Gaza has revealed anything about current Canadian politics, it's hardly Stephen Harper's over-my-dead-body support for Israel or Justin Trudeau's smile-be-happy habit of steering clear of controversial issues. Both the Liberal and Tory leaders have acted quite predictably.

No, what's truly revealing is how Mr. Mulcair has all but silenced the pro-Palestinian hysterics within his party. The party's stand on Israel's shelling of Gaza, while more moderate in tone, largely lines up with the Harper government's position.

Some NDP activists feel betrayed, particularly in Quebec, where devotion to the Palestinian cause remains an article of faith on the political left.

Mr. Harper and Foreign Affairs Minister John Baird have been out front and unapologetic in their defence of Israel and denunciation of Hamas, to the point of being accused of sacrificing Canada's reputation as an honest broker to curry favour with Jewish and evangelical voters.

Mr. Trudeau, meanwhile, issued a short statement on July 15 calling for a ceasefire in Gaza, while asserting Israel's right to defend itself and denouncing Hamas as a terrorist organization. But the Liberal Leader has not spoken publicly and his normally hyperactive Twitter feed has avoided Gaza altogether, except for expressing support for the uncontroversial idea of bringing injured Palestinian children to Canada for treatment. Instead, he's been tweeting praise for Canada's tennis players.

Mr. Mulcair, by contrast, has repeatedly gone out on a limb on Gaza.

"The firing of rockets by Hamas and Islamic Jihad militants at civilian populations is utterly unacceptable," he said in a July 22 statement. "Hamas is a recognized terrorist organization and Israel has the right to defend its citizens from these attacks, while doing its utmost to protect civilians."

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The new NDP language partly stems from the party's quest to look more mainstream in its larger quest for power. But it also reflects its leader's personal commitment to the Zionist cause. Mr. Mulcair's French-born wife is a descendant of Sephardic Jews expelled from Spain during the Inquisition.

"My in-laws are Holocaust survivors. Their history is part of my daily life. That's why I am an ardent supporter of Israel in all [international bodies] and circumstances," Mr. Mulcair told francophone Jews in Montreal in 2008.

Mr. Mulcair was also the first to denounce NDP MP Libby Davies, who, in 2010, appeared to question Israel's very right to exist. She also stated her personal support for a boycott of Israel, defying official party policy.

"To say that you're personally in favour of boycott, divestment and sanctions for the only democracy in the Middle East is, as far as I'm concerned, grossly unacceptable," Mr. Mulcair said then.

Ms. Davies, who remains deputy NDP leader, has confined her comments during the current Gaza conflict to social media, using Twitter to urge Canadians to "speak out." But it's clear Mr. Mulcair's position is ruffling feathers, compounding accusations he has "muzzled" pro-Palestinian voices within the party.

The NDP is not the only progressive party dealing with internal dissension over Gaza. Green Party president Paul Estrin was forced to resign this week after writing, in a blog post on the party web site, that "Gazan officials tell their people to be killed while they hide in bomb shelters."

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But the political stakes are far higher for the NDP, and nowhere more so than in Quebec. It won 59 seats there in 2011, replacing the pro-Palestinian Bloc Québécois as the dominant federal party in the province. It currently retains 56 Quebec seats and holding on to most, if not all, of them is critical to its chances of forming a government in 2015. Will Mr. Mulcair's support for Israel get in the way of that goal?