The letter reiterated Trump’s complaints about dairy quotas, fentanyl and the U.S. trade deficit, which is mostly fueled by American refineries’ thirst for Canadian oil. His social media post caused the Canadian dollar to immediately tumble, indicating the market wasn’t expecting this escalation.

A day after US President Donald Trump announced a new 35 percent tariff on Canadian goods set to take effect next month, Canadian Prime Minister Mark Carney said the country had made "vital progress" in combatting fentanyl,