David Shribman is the former executive editor of the Pittsburgh Post Gazette.

Once again, a lesson from across the border.

Not universal health care; the Canadian system is a disaster and access to a family doctor is as elusive as a Stanley Cup in Toronto, whose Maple Leafs haven’t won hockey’s ultimate crown in 57 years. Not euthanasia; the Canadian Medical Assistance in Dying option is a step too far for the United States, a country that can’t even agree on when life begins. Not even poutine; a nation where 39.6% of adults are considered obese doesn’t need to add beef gravy and cheese curds to its lunchtime routine.

Instead: an open letter from Canada’s artistic, media, economics, business, religious and educational leaders who say they are troubled that “a growing number of us no longer consider it part of a common Canadian value system to put aside our differences and work alongside those with whom we disagree in the broader interests of Canada.”

The implicit message: Don’t let Canada become the United States.

It’s a message as old as 1775, when British settlers in what is now Canada looked with disbelief and disdain at the American rebellion against the mother country. Or as old as 1861, when Canada West Reform leader George Brown said, amid the passions and hostilities of the Civil War, “We are glad we are not them.”

More recently, Rob Goodman, a former Capitol Hill speechwriter who now teaches politics at Toronto Metropolitan University, wrote a book titled “Not Here: Why American Democracy Is Eroding and How Canada Can Protect Itself” in which he worried that “the forces that produced Trumpism in America are on the move here, too: the same political vocabulary, the same collective imagination, the same conspiracy theories, the same funding sources.” Goodman spoke of “the same difficulty, among the political class in both countries, in imagining a constructive response to those forces, beyond the sledgehammer of law enforcement.”

The Canadian leaders’ statement begins by acknowledging that “whether they are connected to geopolitical events happening thousands of kilometers away or derived from homegrown causes, one cannot deny that tensions are on the rise in our streets and on our campuses.” In a direct response to this worry, it calls on current political figures “to address urgently the rise of incivility, public aggression and overt hatred that are undermining the peace and security of Canadian life” and argues, “This issue is so important that it transcends partisanship.”

The rot now is transcending the boundary.

“It is a style of politics that has been validated by what is going on in the U.S. and is adopted by people who don’t seem to have any other way of expressing their thoughts,” said Pierre Martin, a University of Montreal political scientist. “It is present here and amplified because those people have no filter, no shame. American politics has become a circus.”

These Canadian grandees are determined that the circus doesn’t become a road show with a permanent presence across the border.

“Canadians appear increasingly unwilling, unable or ill-equipped to talk to or live peaceably alongside those with divergent views of complex and divisive issues including, as in the current instance, those with significant geopolitical overtones and implications,” they said, adding, “Canadians with different perspectives and lived experiences need to be working together instead of retreating to the familiarity of our echo chambers to lob hurtful tropes at one another. Those who want to speak up for peace and justice should feel safe and empowered to do so rather than chilled into silence. Those who just want to go about their lives without taking a public position on a particular conflict should also feel free to do so.”

The civility that these Canadians are trying to preserve never has had deep roots in the United States, which began as a rebellion against Great Britain and, more broadly, against European notions of court life, where dukes, barons and lesser gentry were required to show ritualized politeness toward the monarch.

“The revolutionaries of the 1770s attacked everything about courtly politics and monarchy as corrupt, decadent, even degenerate,” said Jason Opal, an American who teaches U.S. history at Montreal’s McGill University. Political rebellions in the 1830s, 1870s, 1890s, 1930s, 1950s, and since 2008 were examples of what he calls “a popular, populist strain of American politics has taken some pleasure in mocking and defying the polite, civil traditions that are both necessary to good government and yet still derived from the European court.”

What to do to halt the rot?

Those who signed this open letter wrote that they were “calling upon you, the senior political leadership of Canada, to put political affiliation and partisanship aside and demonstrate your shared commitment to fostering a safer, more cohesive and respectful Canada, where hatred has no home.” Then they got specific.

They urged the country’s leadership and its scholars to undertake a serious examination of what they described as “the causes, scale and impact of issue-driven tensions and conflict in Canada.” They pleaded for support for initiatives “to confront hate and reaffirm the commitment of Canadians to mutual respect and peaceful engagement.” They called for work to “instill in all generations of Canadians respect for and the ability to engage in constructive intercommunity dialogue.”

All very Canadian. But all very applicable to American life today, too.

“There is no doubt that American political culture is more rude, crude and vulgar than its Canadian counterpart,” Mr. Opal said. “The degree of difference between the two countries in this respect has long varied, but the U.S. has almost always been the less civil of the two.”

So I’ve substituted the word “American” for “Canadian” and “the United States” for “Canada” in the following passage and am giving America’s political class an important assignment:

“Speak out wherever and whenever you can about the values that bind us together as a country. Remember and remind all of us of the real danger that the fabric of American life and society could be torn apart, perhaps irreparably, if we continue without intervention down the current path of public hate, violence and vitriol. This is a clarion call for our collective future. The investments that we make, the skills we develop and the values we embody today will help us live up to the promise of the United States. We hope you will respond with the demonstration of leadership and determination that we believe these issues warrant.”