Standing in Ottawa on Saturday morning, hours after the American duties landed, Mark Carney said Canada would match them dollar for dollar. The targets: American steel, dairy, appliances, agricultural equipment, pulp, paper, electronics. The start date: September 8.

That date is the interesting part of the announcement.

Retaliation that begins immediately is punishment. Retaliation scheduled seventeen days out is an offer. Everything between now and September 8 is a negotiating window that Carney has created for himself without appearing to concede anything, and the composition of the list keeps the window open. Steel and agricultural equipment hit exporters in states that pay attention to trade policy. Dairy is the mirror image of the American grievance, aimed squarely back at the sector Washington named first. None of it is calibrated to maximize damage to the Canadian consumer, which is the constraint every retaliating government actually works under.

The duties took effect at one minute past midnight on Saturday, after three days of talks in Washington ended without a deal. Fifty percent, on roughly twenty billion dollars of Canadian goods, with no expiry date attached and no exemption for products that comply with the continental trade agreement the two countries signed and ratified.

Twenty billion sounds enormous until you put it against the denominator. Canada sent the United States something like three hundred and seventy billion dollars in goods last year. The tariffed slice is a bit over five percent of that. Nobody’s economy turns on it.