The 2015 election was, Elections Canada now tells us authoritatively, a break with decades of elections before: Millions more came out to cast ballots, and young people voted in dramatically higher numbers.

Elections in Canada will never be the same.

The Elections Canada data aren't a complete shock. We knew on voting day last October that millions more had come out to vote, and it was no secret that higher turnout among young voters helped propel Justin Trudeau's Liberals to power.

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But now we have reliable estimates of how exceptional this moment was.

Turnout among those between the ages of 18 to 24, for example, rose to 57.1 per cent in last October's vote from 38.8 per cent in 2011. There were almost 1.2 million more voters under the age of 35 – enough, in theory, to swing results in an election in which 17.7 million cast ballots.

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That is extremely significant, not just because of what happened, but what it means for election campaigns.

It's clear that Mr. Trudeau's campaign managed to bring out voters with a message of change, the idea of generational shift and a sense of hope – capitalizing, too, on voters tired of nine years of Stephen Harper. Women and younger voters, in particular, turned out in greater numbers and helped Mr. Trudeau win.

But what it means for future campaigns is even more important.

It is possible to bring new voters into the voting pool, to motivate them to cast a ballot, rather than fighting over a small number of uncommitted folks in a static and dwindling voter pool of less than 60 per cent of the population, and falling.

David Herle, who managed campaigns for former Liberal prime minister Paul Martin and current Ontario Premier Kathleen Wynne, recalls viewing the federal electoral battles as trench warfare between Conservatives and Liberals for a three- or four-percentage-point advantage among a pool of likely voters that is roughly half the population. That meant the issues tended to be geared to older voters, too.

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But it also had an impact on tactics. In a static, low-turnout world, parties might do better by motivating their existing supporters to cast a ballot than trying to win over the other party's supporters. Karl Rove, a strategist for George W. Bush, used that approach, hardening the conservative message to fire up Republican voters. Mr. Harper's Conservatives did some of it in Canada. At other times, parties tried to safely hug the centre, hoping to share those middle voters.

But the calculation is changing.

"All those strategic plays could be swamped by an increase of turnout," Mr. Herle said in an e-mail. He added: "So the rise in turnout among younger cohorts was really a seismic shift."

Last fall wasn't the first time something like this has happened. In the United States, Barack Obama's 2008 presidential campaign showed that bringing in new voters was possible, and a winner. His appeal was a hope-and-change message and, for some, the historic prospect of electing the first black president.

Mr. Trudeau echoed a lot of those hope-and-change tones last year. But other recent campaigns have seen turnout rise with less change. In Ontario's 2014 election, turnout rose, helping both Ms. Wynne and the NDP. It was a campaign with a stark narrative, with Progressive Conservative Tim Hudak advocating cutbacks – but Ms. Wynne didn't stick to a stay-the-course incumbent's message; instead, she portrayed herself as an activist, seeking to motivate voters.

It's not necessarily a liberal-left tactic: Donald Trump claims to have brought new voters into the Republican Party for the primaries. Whether he loses many others in the general election is the key test.

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Perhaps it is partly new politicians with new messages overturning the turnout trend. But a big part is there are new ways to channel the campaign to groups of voters – especially young people – through YouTube, Twitter and other social media. Campaigns, starting with Mr. Obama's, used them.

Tom Pitfield, who spearheaded Mr. Trudeau's digital campaign, told the Liberal convention in Winnipeg last month that the team counted about 50 people at its peak, who created new messages for social media, then used data to test who responded to what, and refine the message. The Liberals digitally identified a million supporters in the last week of the campaign, and urged them to vote. Those are the mechanics, but what matters is the possibility: Parties can motivate new voters, so they have to change the way they campaign.