The Conservative leadership campaign has become a debate over immigration. Resolving that debate could determine the party's future. Because immigrants decide elections.

In every campaign since 1968, with the single exception of 2006, the party that dominated the broad band of suburban ridings surrounding Toronto formed the government. Most of those ridings have large concentrations of immigrants.

But strategists report that the typical Conservative Party member is white, male and over 60. Some of them are sympathetic to the nativist arguments that vaulted Donald Trump into the American presidency.

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What, exactly, are the values that animate the Conservative candidates when it comes to immigration? What changes would they make to the system, as prime minister? In essence, the debate pits Kellie Leitch against the rest.

Dr. Leitch, a pediatric surgeon and MP for Simcoe-Grey, north of Toronto, galvanized the campaign by declaring that every immigrant entering Canada should be subject to a face-to-face interview and screened for "Canadian values," which she defines as a commitment to freedom, equality of opportunity, hard work and generosity.

"I do believe that we should sort of slow it down" so that "we can make sure that the individuals who are coming into our country share our values … and to integrate the immigrant better," she told The Globe and Mail.

Such a lengthy procedure would likely decrease the number of immigrants admitted to Canada, each year, while also increasing the costs of admitting them. On the latter point, "my intent will be to transfer the cost to the immigrant," Dr. Leitch revealed.

Chris Alexander, who was immigration minister in the third Harper government, offered a "back-of-the-envelope" estimate of $1,000 per immigrant to implement Dr. Leitch's plan.

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He advocates the opposite approach: increasing the intake to a maximum of 400,000 new arrivals a year, 70 per cent of them economic immigrants, provided economic conditions warrant.

This figure is well above the 250,000 target set by prime ministers from Brian Mulroney to Stephen Harper and the 300,000 target that Justin Trudeau's Liberal government has set.

"I see the whole question of immigration as a component of our economic policy," he said. Young entrepreneurial immigrants, Mr. Alexander said, slow the aging of the population and generate economic growth.

Maxime Bernier, who represents the Quebec riding of Beauce, would reduce immigration numbers back down to 250,000.

Immigration "has to be done organically and gradually," he said. "When it happens too fast, it creates social tensions and conflicts, and creates a political backlash, as we can see today in several countries."

Others (not all of the 13 candidates were interviewed for this story) avoided setting a target, saying that such quotas are arbitrary and that the real focus should be on recruiting as many immigrants as are needed to fill skills gaps in the labour force.

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Focusing on "the actual number misses the point," said Michael Chong, who represents the Ontario riding of Wellington-Halton Hills. "We need an evidence-based policy on immigration that puts Canada's economic interests at the forefront," he maintained.

There was general agreement that the temporary foreign worker (TFW) program needs to be overhauled to make it easier for employers to recruit temporary workers when Canadians are not available, while ensuring qualified Canadians aren't passed over in favour of foreigners.

Erin O'Toole, who represents the Greater Toronto Area riding of Durham, would like to see the program scaled back.

"We allowed the TFW to become a permanent Band-Aid, and that's what I want to stop," he said. Instead, resources should focus on training or retraining Canadian workers to eliminate labour shortages, while encouraging permanent immigrants to settle in regions, such as the Maritimes, with stagnant economies at risk of population decline.

The Conservatives were damaged in the last election by refusing to support a major airlift of Syrian refugees, even as the Liberals won popular support by vowing to bring in 25,000 almost immediately.

Now, Conservatives maintain, many of those refugees are struggling to find housing, jobs and language training. "The Liberals are using a devastating tragedy for political purposes," Regina MP Andrew Scheer said. He and other candidates think Canada's refugee policy should focus on private rather than government sponsorship, to help refugees integrate more successfully.

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Mr. Bernier would end Canada's involvement with the United Nations in refugee selection. "Civil-society groups that work on the ground have a much better grasp of who could successfully integrate into Canada than a big international bureaucracy," he maintained.

None of the other candidates supported Ms. Leitch's vow to screen every immigrant for anti-Canadian attitudes.

"When Kellie talks about values tests, that's going to be a hard sell for somebody who wants to come and set up a software company, but who won't come if they're going to get questioned about whether they're Canadian enough," Lisa Raitt, who represents the GTA riding of Milton, said. She endorses an immigration policy that's flexible and responsive in meeting local economic needs, while maintaining a refugee program based on humanitarian principles and a temporary foreign workers program that is targeted and flexible.

But Mr. Bernier and Mr. Scheer do support some increase in screening. "I absolutely believe that we have core Canadian values that we need to promote and protect and defend," Mr. Scheer said, though he questioned the "practicality" of Dr. Leitch's approach.

Under Stephen Harper, the Conservatives enjoyed broad support from immigrant Canadians, many of whom are economically and socially more conservative than many native-born Canadians.

But when the party promised during the 2015 election campaign to root out "barbaric cultural practices," it made Conservatives look anti-immigrant.

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New Canadians will support the Conservatives, but only if they believe that Conservatives support them.