With 14 candidates in the Conservative leadership race trying to attract new supporters, the party's membership roll has the potential to be larger than ever. But so far, it seems the number of people eligible to vote in May will be smaller than when the party picked Stephen Harper as leader in 2004.

"There (are) going to be fewer memberships sold in this membership race compared to 2004," candidate Michael Chong said last week at the party's caucus meeting in Quebec City. And he's not alone in this assessment.

Why?

In 2004, the Conservative Party was new. It had just merged the lists of its legacy parties, the Progressive Conservative party and the Canadian Alliance (previously the Reform Party.) Over 250,000 members were eligible to vote.

Stephen Harper, centre, defeated Tony Clement, left, and Belinda Stronach to win the Conservative Party leadership in 2004 by a large margin. The 2017 vote will feature the same weighted ridings and ranked ballot system that elected Harper, but the way the party is selling memberships has changed. (Jonathan Hayward/Canadian Press)

"Canadians were quite upset with the Liberal government of the day because of the … [sponsorship] scandal," Chong said. "There was an incentive for people to join the Conservative Party to get rid of the Liberal government."

Today, it's different. Conservatives just spent a decade in power, with all the bumps and knocks that brings.

Party estimates tally the current membership at just over 100,000. This figure is growing, as lapsed members renew to vote and candidates' teams sign up new supporters.

But Chong said he'll be surprised if there are 150,000 eligible voters on May 27 when the party picks its new leader. That figure might be a bit conservative, but no one CBC News spoke to expects much more.

$15 to join

Controversy erupted last year over the party's decision to hike annual membership fees to $25 from $15.

Jason Kenney — who considered running for the federal leadership before deciding to run for the Alberta Progressive Conservative leadership instead — and Deepak Obhrai, who did join the race, were among the loudest voices calling the fee hike a disincentive.

The party relented. The fee is still $15.

But something else has changed.

Candidates are no longer free to sign up and pay for large blocks of new members using campaign funds. Individuals have to buy their own membership using a credit card or cheque.

Clement joined the Conservative leadership race last July but dropped out later in the year. Selling memberships under the new rules is harder now, he found. (Chris Young/Canadian Press)

"It's comparatively difficult to sign up people," said Tony Clement, once a candidate himself but now working on Maxime Bernier's team.

"If you're doing a phone bank ... your next question is great, give me, a stranger, your credit card information so I can get you signed up. It's not going to happen."

Clement called the rules "impediments to massive signups."

Candidate Andrew Scheer doesn't mind them, arguing they protect the integrity of the race by preventing the shenanigans of Tory races past.

When someone buys a $15 membership, the party "can count on that person to help in an election, show up at events, to make donations down the road," he said.

Scheer's focusing on finding local activists who know how to organize and work networks to sell memberships to motivated supporters.

Andrew Scheer thinks making people pay for their own memberships builds a stronger relationship between the party and its members. (John Woods/Canadian Press)

"It is a challenge. It's a big country," he said. Plus, every riding counts equally: winning a riding with only a few dozen members is as valuable as one with thousands.

Liberals vote for free

The Liberal Party had a different strategy when it elected Justin Trudeau leader in 2013.

A free "supporter" category helped add more than 130,000 new eligible voters, swelling party ranks to over 300,000.

Just over one-third voted, comparable to the 37 per cent turnout Conservatives had in 2004.

Conservative leadership candidate Michael Chong thinks it's time for his party to scrap its membership fees and focus on attracting more people to participate in party politics. (Liam Richards/Canadian Press)

If only one-third cast a leadership ballot in 2017, as few as 50,000 Conservatives spread across 338 ridings will have decided the race.

Chong says Liberals got ahead of the curve.

My vision is of a party that has a million members. A party that has much greater public participation. - Michael Chong, Conservative Party leadership candidate

"Things have changed a lot in the last 10 years," he said. "Increasingly, Canadians are unwilling to pay a membership fee to join a political party. Just like they're not willing to pay a membership fee to sign up to Facebook or have a Gmail account or to sign up to Twitter."

Chong wishes the party would ditch membership fees and create a permanent registry instead, perhaps through a tick box on federal tax returns.

"My vision is of a party that has a million members," he said. "A party that has much greater public participation."

Deadlines soon

After the end of February, a $5 charge applies for memberships submitted up to the final March 28 deadline.

That means if a candidate sells 10,000 memberships in the home stretch, he or she will have to fundraise $50,000 more.

(As an incentive, the party paid campaigns $5 for each membership sold before October.)

Which brings us to Kevin O'Leary, who joined the race Jan.18 promising to draw on the support of 40,000 people urging him to run.

Kevin O'Leary's late entry into the Conservative race limits his time available to sell memberships to new supporters. His donors may also contribute up to the $1,500 maximum for only one calendar year, 2017, instead of also being able to contribute the same amount in 2016. (David Donnelly/CBC)

Spokesman Ari Laskin didn't offer CBC News specific numbers but said there was "a real surge of membership purchases on our website."

Earlier this week, O'Leary told The Canadian Press he's signed up 9,000.

He may be the first choice of some existing members. If he isn't, he's got a long way to get over the 50 per cent threshold to win.

"He's starting late, and he'll have his work cut out for him," Scheer said.

Chong, Kellie Leitch and fundraising front-runner Maxime Bernier started selling memberships last spring.

"O'Leary has stated that he's going to be relying on the hundreds of thousands of people who follow him on Twitter or Instagram to be sign-ups. A lot of those people are Americans," Clement said.

This is not the system that elected Donald Trump, he warned.

"We don't have a primary system where each province is deciding on a different day and someone can gain momentum," Clement said. "No one knows how other people are voting until after the votes are counted.

"He should be able to sign up some members. Whether that's enough to win the race is an open question that we'll all be experts about after it happens."