Prime Minister Mark Carney has some explaining to do.

On Wednesday, he told the New York Times that he had examined the possibility that U.S. President Donald Trump might order military action against Canada, a scenario Carney described as an “extreme tail risk.” In plain English, he was talking about an event he considers extremely unlikely but serious enough to prepare for.

Preparing for unlikely threats is part of responsible government. Publicly raising the possibility that Canada’s closest ally might invade us is another matter.

So why did Carney do it?

Trump has given Canadians plenty of reasons to question our relationship with Washington. He has repeatedly talked about Canada becoming the 51st state and used tariffs and economic threats against us. But when asked directly in January 2025 whether he would use military force to acquire Canada, Trump said no. His preferred pressure, he said, was “economic force.”

Canada would be foolish to ignore Trump’s rhetoric and economic threats, but there is a big difference between an American president threatening Canada’s economy and an American president threatening to invade Canada.

Canada and the United States are not simply neighbours. We have worked together through NORAD, the joint military command responsible for defending North America, since 1958. Carney is publicly discussing the possibility of military action by the country Canada has relied on for decades as the cornerstone of its continental defence.

Earlier this year, Canadians learned that the military had modelled a hypothetical U.S. invasion. That may sound ominous, but militaries routinely consider unlikely scenarios as part of contingency planning. The exercise was conceptual and theoretical, not an actual military plan.

But the military’s contingency planning is not the issue. Carney has now given that remote scenario something it did not have before: the public attention of the prime minister himself.

Carney’s remarks also came as he was arguing that Canada must reduce its economic and strategic dependence on the United States, including its reliance on American military technology.

Portraying the United States as a potential military threat does, however, change the political calculation in Ottawa. Major shifts in defence, trade and foreign policy become easier to sell when they can be presented as necessary to protect Canadian sovereignty.

We don’t know whether that was Carney’s intention. But a prime minister should not publicly elevate the possibility of war with Canada’s closest ally without a compelling reason.

If Ottawa has evidence suggesting the threat has become more serious, Carney should say so. If it doesn’t, he should explain what Canadian interest was served by putting such an extraordinary possibility into the public conversation.