Trudeau called it "extraordinarily fitting" that the meeting should occur on the same "auspicious" day that the charter was adopted 31 years ago — a seminal addition to the Constitution when it was patriated in 1982 by Pierre Trudeau.
"We celebrate today, as Liberals, the document that makes sure that Canadians enjoy freedoms that can never be taken away," he told Liberal MPs and senators.
In an era when parties are elbowing each other for room at the centre of the political spectrum, Trudeau asserted that the charter is what distinguishes Liberals from the Conservatives and NDP.
"(The charter) is at the centre of what it means to be a Liberal," he said.
"Conservatives talk a good game about being a party of freedom but they are mistrustful of the mechanisms that actually ensure those freedoms for Canadians and that's why they don't celebrate the charter."
The Harper government issued a perfunctory press release last year to mark the 30th anniversary of the charter, in stark contrast to the year-long, government-sponsored festivities to mark the 200th anniversary of the War of 1812.
New Democrats supported patriation of the Constitution with a charter of rights back in 1982. But Trudeau asserted that the NDP finds itself "deeply conflicted" today.
"(That's) largely because of a political calculation they've made, pandering to a tremendous number of very vocal sovereigntist Quebecers who do not particularly appreciate the Charter of Rights and Freedoms."
NDP Leader Tom Mulcair called Trudeau's assertion "completely false."
"There has never been the slightest hesitation (among New Democrats) with regard to the importance of the charter, for the rights that it protects for all Canadians."
His office later issued a statement noting that NDP founding leader Tommy Douglas introduced the country's first bill of rights, in Saskatchewan in 1947. It also said NDP premier Alan Blakeney and federal leader Ed Broadbent "worked to create the charter with Mr. Trudeau's father."
Mulcair said the NDP, which swept Quebec in the 2011 election, is committed to creating "winning conditions for Quebec within Canada. It's unacceptable, he added, that "one of the key founding provinces ... should be excluded from the Constitution."
The Constitution was patriated over the objections of Quebec's separatist government of the day and has been a sore point with many Quebecers ever since.
Nevertheless, Trudeau said no document is more broadly supported "by all Canadians, including the vast majority of Quebecers" than the charter.
Wednesday's flare-up between Trudeau and Mulcair signals what promises to be a pitched battle for the hearts — and votes — of Quebecers in the next election. Trudeau has indicated that the Liberal party's route to redemption runs straight through Quebec.
His arrival on the scene, after winning the leadership in a landslide Sunday, has triggered a chippier tone from the Conservatives as well.
The governing party launched attack ads against Trudeau on Monday, suggesting he lacks the judgment and experience to be prime minister.
On Wednesday, Prime Minister Stephen Harper criticized Trudeau for suggesting one needs to look at the root causes of the tragic bombings in Boston.
And, in a response to a Trudeau query about government plans to celebrate the charter, Canadian Heritage Minister James Moore launched an unrelated line of attack, accusing the Liberal leader of stealing jobs from his constituents by urging the government to allow a restaurant in his riding to hire chefs from China.
"Why is he writing letters to bring in Chinese workers in the food industry in Montreal rather than helping us create jobs for Canadians in Montreal?" Moore demanded — a curious argument for a government that has expanded the temporary foreign worker program in a bid to close the so-called skills gap.
A copy of the four-year-old letter referred to by Moore — written by Trudeau to the Canadian embassy in Beijing — mysteriously surfaced on Twitter shortly thereafter.
With polls suggesting the leadership race has boosted the Liberals back into contention, Trudeau was welcomed as the conquering hero by Grit MPs, senators and staffers at the morning caucus meeting. They crammed into the tiny room in the bowels of Parliament's Centre Block where the party has been relegated since being reduced to a third-party rump in the 2011 election.
Trudeau predicted the party has "not just a glorious past but a glorious future." Still, he soberly told the assembled Grits: "We have an awful lot of work to do."
On his third full day on the job, Trudeau began slowly putting his stamp on the party apparatus, assigning shadow cabinet roles for former leadership rivals Joyce Murray and Marc Garneau and for Bob Rae, who held down the Liberal fort as interim leader for the past two years.
Rae will resume his former role as foreign affairs critic, while Murray returns to her role as Asia-Pacific and small business critic and Garneau takes on the natural resources post.
Trudeau won't shake up the rest of the shadow cabinet until after Parliament breaks for the summer in late June.
He also named Cyrus Reporter — an Ottawa lawyer, veteran political operative and one-time chief of staff to former minister Allan Rock — as his new chief of staff.
Katie Telford and Gerald Butts, who led Trudeau's leadership campaign, will now focus on preparing for the next election in 2015 and won't be joining his office staff. However, both will continue to be influential advisers.
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