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As a practical matter, this is a pretty small change: The system runs smoothly, and appeals are less important than they used to be, at least in some people’s eyes. And there’s always the World Trade Organization, with its own dispute resolution process, as a backstop.

But practical matters aren’t the point. Many Canadians believe that Mexico caved to Mr. Trump, putting Canada in a precarious position as the outlier. The real issue here, as before, is the power imbalance.

The dispute-resolution issue is similar to the other main obstacles facing negotiators: Canada’s protection of its culture and dairy sectors. Canadians are intensely protective of their culture, especially when it is so close to, and so often overshadowed by, the United States’. Because the original trade deal included protections for what Canada considered the critical pieces of its cultural heritage, Ottawa has insisted that such protection be maintained in any new deal; Washington, obviously, disagrees.

Dairy is also a case where the principle may seem more important than the practical. Canada sets domestic prices for dairy products; for this to work, it needs to place limits on how much milk and cheese it imports. Canadian negotiators are willing to loosen up on some of those limits, as long as the country’s command-and-control system survives. But that system is exactly what Mr. Trump has attacked with his tweets about “270 percent tariffs,” which in fact are rarely applied.

In other words, the reason these talks have been so hard is that the two sides see them in fundamentally different terms. To Americans, Canada seems to be making a big fuss over minor details. To Canadians, Americans — and Mr. Trump above all — seem intent on undermining hard-fought protections.

Canada is perfectly happy to negotiate changes to Nafta; in fact, they’re overdue. The negotiations should have been about working together in the digital age. A deal should simplify rules of origin and align regulations for trade in goods, as well as focus on trade in services. It should open up government procurement and clarify intellectual property rules. Some of these are in play, but they’re hardly anyone’s priority.

Thirty years ago, Prime Minister Mulroney was intent on deepening trade relations with the United States. Now Prime Minister Trudeau has named a minister of international trade diversification. Diversification from what? No one in Canada need ask.

Drew Fagan is a professor at the Munk School of Global Affairs and Public Policy, University of Toronto, and a former head of policy planning at Canada’s Foreign Affairs Department.

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