Mr. Trudeau came to power in 2015 on the promise of a new, revitalized Liberal Party, removed from the stale old boys’ club of yore. The party, though it imagines itself as representing the quintessential ideals of Canadiana, has a long track record of corruption and chicanery, particularly in Quebec.

With an electoral base in the country’s most heavily populated regions, like Quebec, the Liberals have enjoyed many decades in power. It is not without merit that they are referred to, derisively, as Canada’s Natural Governing Party.

Power brings with it certain habits. This is true everywhere, but in a democratic country with a population the size of California spread across a gigantic landmass, influence runs in a geographic network that we describe in shorthand as the Laurentian Elite, after the St. Lawrence River that runs through eastern Canada. Mr. Trudeau, the son of former Prime Minister Pierre Elliott Trudeau, is very much a creature of this elite.

And so is SNC-Lavalin. Not just any company gets its calls taken by the prime minister’s office. Founded in 1911, SNC-Lavalin is a crown jewel in the Quebec corporate firmament. The company’s lobbyists have long ties in both Conservative and Liberal governments. Its lawyers include a former Supreme Court justice. A retired senior federal official is on its board. One of its corporate directors also sits on the board of the Trudeau Foundation. Quebec’s public pension funds own about 20 percent of SNC-Lavalin’s shares.

The decision about SNC-Lavalin’s case was being made in the lead-up to Quebec’s Oct. 1 provincial election — and that was apparently on the prime minister’s mind. According to Ms. Wilson-Raybould’s testimony, senior staff members from Mr. Trudeau’s office said the company was threatening to relocate to London if it did not get the plea deal. One such staffer, she said, told her “if they don’t get a D.P.A., they will leave Montreal, and it’s the Quebec election right now, so we can’t have that happen.”

Ms. Wilson-Raybould recounted a conversation with Mr. Trudeau: “At that point the prime minister jumped in, stressing that there is an election in Quebec and that ‘I am an M.P. in Quebec — the member for Papineau,’” she said. When she asked if he was trying to override her independence as attorney general, she said, the prime minister replied, “‘No, no, no, we just need to find a solution.’ ”