On Monday, Canadian Prime Minister Justin Trudeau came forward with a shocking allegation: that “agents of the government of India” had assassinated a Canadian citizen on Canadian soil. The man, named Hardeep Singh Nijjar, was killed in British Columbia back in June. He was a global leader in the Sikh separatist movement, which called for an independent state on land currently inside the Indian state of Punjab. New Delhi had previously alleged that Nijjar was not merely an activist, but a militant involved in terrorist plots. Now he’s dead — and the Canadian government believes India is responsible. It is...