Justin Trudeau put his leadership on the line Saturday with a direct appeal to grassroots Liberals to accept his controversial proposal aimed at transforming the ruling party from an exclusive club into a wide-open political movement.

The prime minister's intervention, combined with some eleventh-hour amendments, produced the desired result: 1,988 delegates at the party's first national convention since taking power last fall voted for the proposal, just 66 against.

But the result had not been assured just 24 hours earlier, when hundreds of rank and file Liberals complained bitterly that they felt they were being bullied into supporting a proposal upon which they hadn't been consulted and which many felt was a naked power grab by the leader and his cronies on the party's national executive.

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Despite the potential risk, Trudeau took full ownership of the proposal for a new, streamlined party constitution which would, among other things, do away entirely with the concept of membership.

Trudeau used a speech a couple of hours before the vote to address delegates' qualms.

He later personally moved the motion asking for support for the constitution.

"If I believed for a second that the new constitution was about taking power away from the grassroots, I would be right there with you, shoulder to shoulder, speaking out against it," he told the convention.

"But it isn't and it doesn't."

Indeed, Trudeau argued, the new constitution is all about "closing the distance between the leader and every single contributor to this movement we've built."

Under the proposal, anyone willing to register for free as a Liberal will in future be entitled to vote in leadership and nomination contests, attend conventions and take part in policy development.

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Some grassroots Liberals had said they felt intimidated by the heavy-handed tactics used to rally support for the proposal, with Liberal MPs and party staffers lobbying hard among the delegates.

That manifested itself Friday in an unsuccessful attempt to change the rules to allow a secret ballot vote on the proposed constitution, where delegates wouldn't feel "pressured one way or the other," as one Liberal put it.

Trudeau directly addressed the allegations of intimidation, telling opponents of the proposal: "It takes courage to speak out against something your party leadership believes in and I want you to know I admire and thank you for doing it."

Trudeau's intervention came after a special question-and-answer session Friday left advocates of the proposal doubtful that it would pass. The session attracted hundreds of delegates, none of them happy about it.

One of the biggest complaints was about the amount of discretion the proposed constitution would give to the leader and the party's national board to devise bylaws governing all manner of party operations, including registration of Liberals, policy development, riding associations and the party's provincial wings and various commissions.

Trudeau, who had been in Japan for the G7 summit during the first two days of the convention, argued Saturday that the current, cumbersome constitution "is a product of the era we worked so hard, together, to put behind us: the era of factional battles and hyphenated Liberals, of regional chieftains and behind-the-scenes power-brokers, of the closed, insular thinking that almost killed this party."

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He called it a "hodge-podge" of 18 different constitutions, including those governing the party's various commissions and provincial and territorial wings.

"It empowers a bureaucracy that creates conflict and distance between us. Most important for me, and for any future leader of this party, it creates distance between the leader and the grassroots."

While there were few objections to the concept of doing away with paid memberships, delegates were concerned that the proposed constitution included no mention of the principles or values that would supposedly bind registered Liberals together.

That was remedied Saturday with one of several amendments, which inserted the preamble from the old constitution into the new one.

In the end, even the founder of a grassroots campaign to defeat the proposal came on side.

"Our party leadership has listened, heard and responded to many of the concerns we expressed," said Kingston riding association president Tom Addison.

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Former interim leader Bob Rae also weighed in, urging delegates to support the new constitution.

"A great political party is not a club, it's not a private organization," Rae said. "It is an organization that's sustained by its relationship to the people around it and the people around us are the people of Canada."

Liberals took the first step down the road to no memberships in 2012, when they decided to allow anyone willing to sign up as a supporter to vote in the leadership contest that elected Trudeau.

Liberals took a "leap of faith" and gave their party, which had been "left for dead as a political force" back to Canadians, Trudeau said, smiling broadly.

"And look at what they've done with the place."