Steamroller, juggernaut, bandwagon – call it what you will, Jagmeet Singh appears to be headed for victory as leader of the federal New Democratic Party, which could transform the party.

A party of labour could become a party of non-unionized but vulnerable workers. A party that was, to be blunt, too old and too white could become more young and diverse. A party of downtown enclaves and hinterlands could become a party of the suburbs.

In a word, Jagmeet Singh could make the NDP competitive.

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On Wednesday, B.C. MP Nathan Cullen threw his support behind Mr. Singh. Mr. Cullen is a formidable force within the party and the caucus. His endorsement reinforces Mr. Singh's strength in British Columbia.

The Brampton MPP also has strong support in the 905, the band of suburban cities surrounding Toronto.

In federal politics, the party that wins the 905 and B.C's Lower Mainland wins the election. You don't need Quebec or Atlantic Canada or the Prairies or any downtown riding. You need the twin suburban heartlands of this mostly suburban country. This is what makes Mr. Singh so much more politically attractive than any other candidate.

(A caveat: Stephen Harper won the 2006 election with little support in the 905. But his Conservative minority government was one of the weakest ever formed. With each subsequent election, his coalition strengthened as his support in the 905 grew, until the Liberals took the 905 away from the Conservatives in 2015.)

Mr. Cullen is not troubled that Mr. Singh is not an MP. It troubles outgoing NDP Leader Thomas Mulcair, who recently said it would be a "heck of a lot better" if the next leader were in the House. But Jack Layton didn't have a seat when he became leader, Mr. Cullen points out.

Winning elections is about more than electoral triangulation. Leaders should stand for something. What does Mr. Singh stand for that would attract suburban voters in the 905 and Lower Mainland?

On economic issues, this personally charming lawyer, style maven and mixed martial arts fighter resembles the left wing of the Liberal Party. A prime minister Singh would increase support for vulnerable workers – who hold the kind of lower-income, less-secure jobs that immigrant and younger workers often get stuck with these days – while increasing taxes on businesses and the rich.

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On foreign policy, he would be more confrontational with U.S. President Donald Trump. In the Ontario Legislature, "I called out the misogynistic comments as unacceptable, the Islamophobic and xenophobic comments as something we should not accept," Mr. Singh said in an interview.

On the environment he would accelerate efforts to fight climate change.

There are plenty of Liberals who wish Justin Trudeau would do all these things.

On one issue, Mr. Singh stands out: During his years as a criminal defence lawyer, he became convinced that the justice system is fundamentally flawed.

"The punitive model has been proven not to work," he says. It "has not been shown to make society safer, it has not been shown to reduce crime rates, it doesn't make the individual any better when they are released from custody." He would reorient the system toward rehabilitation over punishment, which is why he favours decriminalizing drug possession – regardless of the drug.

But many Canadians want criminals to be punished, not rehabilitated, especially for severe misdeeds. To that approach Mr. Singh responds: "Is it making our society a better place? Is it making it a safer place? Is it making it a place where we can all enjoy a better life? If it's not doing that, then I think we need to re-evaluate it." This principled stand could be a very hard sell.

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Your correspondent has a less-than-stellar record when it comes to predicting winners. (Maxime Bernier "is now heavily favoured to become the next leader of the Conservative Party," I wrote in April.)

But if Jagmeet Singh is on his way to becoming leader, then the NDP could present a very different face to the world and to voters.

Immigrant voters. Suburban voters. The voters who decide elections.