The Trudeau government has vowed to cut those numbers and improve the system.

But it won’t budge on what Professor Macklin and others call the bigger issue: the “safe third country” agreement with the United States.

The agreement, drawn up in border-security talks after the terrorist attacks of Sept. 11, 2001, essentially allows Canada to turn back any asylum seekers who show up at regular border crossings, since Canada has declared the United States to be a safe place for refugees. That has led some asylum seekers to try to cross into Canada from the United States “illegally,” to use the government’s term, or “irregularly” as Professor Macklin prefers, particularly in Quebec.

Professor Macklin and others have long rejected the idea that the United States is a safe place to seek asylum. The current border turmoil, she said, has only reinforced that view.

Mr. Trudeau said this week that he had no plans to end the agreement, without offering much in the way of a defense of it.

The agreement is now being challenged in court for a second time. It was struck down in 2008 by the Federal Court but that decision was overturned on appeal.

Professor Macklin, meanwhile, has a more provocative proposal for killing the agreement. “If Donald Trump understood what the first safe country agreement does,” she said — meaning that it pushes immigrants back to the United States — “he would have been the first to suspend it.”