At least one prospective contender, New Brunswick MP Dominic LeBlanc, appears poised to be the first to back away from the pool's edge.
LeBlanc is scheduled to appear with Trudeau on Friday when the presumptive front-runner visits his riding of Beausejour.
"Don't assume," LeBlanc said in an email late Tuesday when asked if he's going to endorse Trudeau, a lifelong friend.
Nevertheless, it is widely assumed LeBlanc will indeed decline to run now that the party's undisputed rock star has jumped into the race.
Most Liberals want to see a vigorous contest, fearful that a coronation will do little to excite Canadians. Even Trudeau's organizers want the prohibitive favourite to be tested, to earn victory rather than feed the perception that he's coasting on the coattails of his late father, former prime minister and Liberal icon Pierre Trudeau.
Trudeau used Tuesday's campaign launch to try to step out from his famous father's shadow, exhorting Liberals to focus on the future, not their party's glorious past.
He warned Liberals there'll be no easy fix or shortcuts on the road to electoral rehabilitation, that even his celebrity, telegenic face and iconic surname won't be enough to revive the fortunes of a party reduced to rubble in the 2011 election.
"I said to Liberals after the last election that we need to get past this idea that a simple leadership change could fix our problems," he told hundreds of pumped, sweaty supporters crammed into a small hall at a community centre in his Papineau riding.
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"I believe that still. My candidacy may shine a few extra lights upon us. It may put some people in the bleachers. But what we have to do with this opportunity is up to us — all of us.
"And when Canadians tune in, we need to prove to them that we Liberals have learned from the past, yes, but that we are 100 per cent focused on the future."
Trudeau later ruled out the one shortcut thought by many to be the party's only salvation: a co-operation pact or merger with the NDP, although he's sent mixed signals on the idea in the past.
"Listen, I'm running to be leader of the Liberal Party of Canada ... because I believe in an option that is not polarized around the edges, that is not bound to an ideology but is looking for the best possible way to serve Canadians," he told reporters after his speech.
"Will the Liberal party in the future work with all parties when it finds agreement? Absolutely. Is there going to be formal co-operations? No."
The launch was a testament to Trudeau's star power. The community hall was filled to its 500-seat capacity and an overflow crowd jammed the hallway. A number of former MPs — Don Boudria, Navdeep Bains, Pablo Rodriguez, Eleni Bakopanos — and at least one current MP — Massimo Pacetti — were among the adoring throng.
Although the faces of some of his father's former cabinet ministers — Marc Lalonde, Andre Ouellet, Lucie Pepin — also dotted the audience, Trudeau made only one passing reference to his father during his 30-minute speech. Indeed, he took pains to stress that his leadership campaign will be "about the future, not the past."
A screen behind the podium displayed a simple campaign logo that featured Trudeau's first name much more prominently than the lineage for which he became famous.
He credited middle-class Canadians with some of the achievements Liberals typically claim as their own, including his father's signature accomplishment: patriation of the Constitution with a Charter of Rights.
And he maintained it's only by reconnecting with the average folk who gave the party life that Liberals will again become the vehicle for their aspirations.
Trudeau singled out restoring the economic health of the Canadian middle class as a principal goal. And on that front, he positioned the Liberals in their traditional role as the pragmatic party of the middle, between the more dogmatic Conservatives and the NDP.
"What's the response from the NDP? To sow regional resentment and blame the successful. The Conservative answer? Privilege one sector over others and promise that wealth will trickle down, eventually," he said.
"Both are tidy ideological answers to complex and difficult questions. The only thing they have in common is that they are both, equally, wrong."
A school teacher before jumping into politics in 2008, Trudeau has long been seen by his critics — many of them fellow Liberals — as a man of more flash than substance. Tuesday's speech was designed to showcase a more cerebral, thoughtful side.
"It is time for us, for this generation of Canadians, to put away childish things," he said. "More, it is time for all of us to come together and get down to the very serious, very adult business of building a better country."
He chose to make his announcement on Tuesday because it would have been the 37th birthday of his late brother Michel, a skier who was killed in an avalanche in 1998.
"Every day, I think about him and I remember not to take anything for granted," Trudeau said in French. "To live my life fully. And to always be faithful to myself."
His surviving brother, Sacha, was at the rally with his three toddlers and will be a key member of the Trudeau's campaign team. He declined to speak to reporters Tuesday.
Trudeau reached out to Quebecers, who switched en masse to the NDP in 2011, promising a Liberal party that "promotes and cherishes the francophone reality of this country."
"I want the Liberal party to be once again the vehicle for Quebecers to contribute to the future of Canada."
Trudeau embarks today on a cross-Canada tour designed in part to prove he's more than just his famous father's telegenic offspring.
He'll kick things off in Calgary, a Liberal wasteland since his father's hated National Energy Program, and Richmond, B.C., before attending a rally Thursday in Mississauga, Ont.
Trudeau has been in the public eye since he was born on Christmas Day, 1971. As a child, he travelled the country and the world with his famous father, then prime minister.
When he entered politics five years ago, he eschewed offers to run in Montreal's Outremont riding — then considered a safe Liberal seat, now held by NDP Leader Tom Mulcair — choosing instead to fight a contested nomination in Papineau, once a Bloc Quebecois stronghold and among the poorest ridings in the country.
He defeated a star Bloquiste in 2008 and bucked the NDP tide that swept Quebec in 2011, increasing his margin of victory.
Trudeau's celebrity has made him the party's biggest draw at fundraisers. He boasts more than 150,000 Twitter followers. His already sky-high stock soared last spring when he won a charity boxing match against Conservative Senator Patrick Brazeau.
For all that, Trudeau remains an unknown quantity in many respects. In his various shadow cabinet posts — youth, amateur sport, immigration — he's had little to say about the big issues of the day, virtually nothing about the economy.
When he's ventured occasionally into meatier issues, he's invariably created controversy —criticizing the government's use of the word "barbaric" to describe female genital mutilation, suggesting he'd support Quebec secession if he thought Canadians shared Prime Minister Stephen Harper's values.
Supporters at Tuesday's rally invariably said Trudeau has been under-estimated, that he's got more depth and substance than he's given credit for.
But comparisons to his father, an incisive intellectual, seemed inevitable.
"Well, of course, his dad was a great, great intellect. But I think Justin is equally a very talented speaker," said Ouellet.
Lalonde said Trudeau is like his father in his commitment to the common good but very different in personality.
"While his father was a fantastic public speaker ... he was not a very warm person in contact one to one, he was a very reserved person, even a kind of a shy person in private. Whereas Justin, on the contrary, is very outgoing."
Toronto-based constitutional lawyer Deborah Coyne, the mother of Trudeau's half-sister, has already announced her candidacy, as has Manitoba paramedic Shane Geschiere.
A host of others are considering taking the plunge but may yet be scared off by Trudeau's entry into the race.
Among them are Montreal MP Marc Garneau, Canada's first astronaut, Vancouver MP Joyce Murray, former cabinet minister Martin Cauchon, former MPs Martha Hall Findlay and Gerard Kennedy, Ontario government economist Jonathan Mousley, former Ottawa candidate David Bertschi, Toronto lawyer George Takach, and David Merner, former president of the party's B.C. wing.
Ottawa MP David McGuinty is also said to be mulling his chances but is not considered likely to take the plunge. Meanwhile, veteran Montreal MP Denis Coderre is pondering whether to run for the Liberal leadership or mayor of Montreal and is thought to be leaning toward the latter.
The contest doesn't officially begin until Nov. 14 and culminates on April 14.
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