When Jagmeet Singh took over as leader of the NDP, he seemed like just the tonic the party needed – young, hip, multicultural, completely Canadian but with a dashing touch. Those turbans! That beard! He was just the kind of figure to make progressive folks feel good about themselves, their party and their prospects. GQ, the men’s fashion magazine, profiled him in rapturous terms, calling him “the incredibly well-dressed rising star in Canadian politics.”

Not many people outside the Sikh community thought too much about the other side –the side that is deeply invested in old grievances and diaspora politics. When the CBC’s Terry Milewski pressed him hard on his views of the 1985 Air India bombing – the worst terrorist attack in Canadian history – Mr. Singh refused to blame the bombing on Sikh extremists. “I don’t know who was responsible,” he said. Mr. Milewski was accused by some of a touch of racism for even raising the matter. No unturbanned politician would have had to endure such a grilling, the critics charged.

But Mr. Milewski was right to ask. This week, reports in The Globe gave details of Mr. Singh’s appearances at two different events promoting Sikh separatism. At one of them, he talked as if India were his own homeland. In a speech he gave there, he accused India of “genocide,” and described it as something that happened to “us.” His use of the first person was striking. He described India as “our country where we live” – a startling use of language for a born-and-bred Canadian politician.

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The diaspora politics of the Sikh community are obscure to most of us. To some, the old wounds feel as fresh as yesterday. That’s certainly the case for Mr. Singh. The “genocide” he cites is the massacre of about 3,000 Sikhs during three days in 1984, in the aftermath of the assassination of Indira Gandhi by two Sikh bodyguards. In an emotional article published Thursday in The Globe, he explained that the terrible persecution of the Sikhs inspired him to stand up for human rights. He likened Indian violence against Sikhs to the pain and trauma inflicted by the residential schools – trauma that endures for generations.

What Mr. Singh didn’t say is that the violence cut both ways. Also in the 1980s, violent Sikh fundamentalists in Punjab sought to form an independent theocratic state called Khalistan. As Canadian writer Gaurav Singhmar notes, that fundamentalist movement “was largely an export from radical Sikh populations in the U.K. and Canada.” It was Sikh militants who blew up Air India Flight 182, killing 329 people – a fact that Mr. Singh had been extremely reluctant to acknowledge until his Globe opinion piece.

The Khalistan movement is largely dead in Punjab. And most Canadian Sikhs want nothing to do with the extremists. But as Ujjal Dosanjh, the former premier of British Columbia explained on the CBC, “it continues to find traction here, due to politicians of all hues playing footsie with Khalistan sympathizers.”

All of this should be deeply troubling, not just to the party Mr. Singh now leads but also to the rest of us. A man who wants to be prime minister is up to his neck in the ethno-nationalist politics of another country and another time and place. He is deeply sympathetic to the more militant wing of his own ethnic community. He is heavily indebted – some say overly indebted – to the Sikh ethnic vote for his job. One reason he won the leadership was that he managed to sign up more than 10,000 B.C. Sikhs as new party members. ”My concern is too many Sikhs have signed up as NDP members because of Singh’s Punjabi identity and because he’s a baptized Sikh,” radio host Harjit Singh Gill told the Vancouver Sun’s Douglas Todd.

You’ve got to wonder how thoroughly Mr. Singh was vetted for his job. Did his beard and bespoke suits bedazzle people into skipping the tough questions? Did anybody worry how the divided politics of the Sikh community would spill over into federal politics? Did anybody worry about the consequences of such a major shift to voting-bloc politics? Or were those questions considered too rude to ask?

All three parties have played footsie with Sikh separatists, of course. Justin Trudeau got in trouble in India because one of them got in the door at a reception. But the role of ethnic politics in Canada needs to shrink, not grow. One of the greatest challenges to multiculturalism is the nurturing of grievances and hatreds imported from afar. We need leaders who will make it clear we won’t tolerate that – not leaders who fan the flames.