Dense smoke from Canadian wildfires is once again choking U.S. cities. President Donald Trump has accused Canada of failing to maintain its forests and has threatened to impose “pollution” tariffs on that country’s exports in response to the health and economic damages inflicted on the public. Michigan Republicans have likewise warned Prime Minister Mark Carney that they are “done accepting apologies,” while Sen. Bernie Moreno of Ohio has raised the prospect of sanctions.

Their frustration is understandable. For years, Americans have watched Canadian wildfire smoke trigger air-quality alerts and place people with respiratory conditions at greater risk. The immediate debate may center on forest management, fire prevention, and Canada’s responsibility to limit cross-border harm. But the episode raises a larger question with implications well beyond wildfires: Why should people bear the costs of pollution produced outside our borders?