Riding in a motorcade as he had as a boy, but never as the center of attention, Trudeau chose his words carefully. ‘‘There was a perception that I’d grown up with a silver spoon in my mouth,’’ he said. ‘‘I’d boxed for 20 years on and off, so I knew that the worst-case scenario was that I was going to take a brutal beating but stay standing until at least near the end. I was confident I could take a punch. I knew I had the stamina to last three rounds. People were saying that maybe he was still smoking while he was training. I was absolutely focused on my training. One thing people are starting to realize is that I work incredibly hard at everything I set my mind to.’’

One year later, the Liberal Party elected him leader, and two years after that, the country elected him prime minister. The scale of Trudeau’s underdog victory was stunning: With a comfortable majority of 184 seats in Parliament, and Liberals in seats spread across the country, he won an undeniable national mandate. As he has managed the transition from campaigning to governing, he has presented an ambitious agenda: funding infrastructure projects to stimulate the economy, supporting programs to reduce childhood poverty, investigating the disappearance and murder of more than 1,000 First Nations women, introducing a rigorous carbon-capture policy, legalizing marijuana. The Canadian system does not have the same checks and balances among branches that the American system does, so Trudeau can implement his policies without being stymied by right-wing opposition.

As an example of his thinking, Trudeau noted his decision to raise taxes on the top 1 percent of earners while lowering middle-class taxes, even as his government funds infrastructure improvements. He knew that Canada would run a deficit, which was unusual for a country known for fiscal probity, but he believed it was the way forward. ‘‘Confident countries are willing to invest in the future,’’ Trudeau said, ‘‘not always follow the conservative orthodoxy of balanced budgets at all costs.’’

In the face of the Syrian refugee crisis, Trudeau had pledged to bring 25,000 civilians fleeing war to Canada by the end of the year — a cry that rallied the nation in his honeymoon days. The shootings in Paris didn’t change this policy, but he has decided to slow the process to ensure it is orderly and safe. (By Jan. 1, 10,000 will be admitted.) But if the Paris or San Bernardino attacks had happened in Montreal or Winnipeg before the election, he may well have lost, an illustration of the fragility of democratic institutions in the age of terror. Trudeau said he wants Canada to be free from the politics of fear and division.

‘‘When a mosque was vandalized in a small rural community in Cold Lake, Alberta — which is as conservative as you can imagine in Canada, with the stereotypes around that — the entire town came out the next day to scrub the graffiti off the walls and help them fix the damage,’’ Trudeau told me. ‘‘Countries with a strong national identity — linguistic, religious or cultural — are finding it a challenge to effectively integrate people from different backgrounds. In France, there is still a typical citizen and an atypical citizen. Canada doesn’t have that dynamic.’’

Terrorist groups have specifically said they are targeting Canada and Canadians. And on the subject of national security, Trudeau’s critics say he’s a lightweight and a dangerous one. Trudeau’s most radical argument is that Canada is becoming a new kind of state, defined not by its European history but by the multiplicity of its identities from all over the world. His embrace of a pan-cultural heritage makes him an avatar of his father’s vision. ‘‘There is no core identity, no mainstream in Canada,’’ he claimed. ‘‘There are shared values — openness, respect, compassion, willingness to work hard, to be there for each other, to search for equality and justice. Those qualities are what make us the first postnational state.’’

Stepping out of the S.U.V., eager to plunge into the crowd, Trudeau seemed like a man at the beginning of a very big, and very uncertain, journey. ‘‘I’m excited to be on the world stage,’’ he said, with peculiar Canadian understatement mixed with dynastic confidence. ‘‘I think people are starting to see that I’m actually reasonably fit for this office.’’