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.

Canadian Prime Minister Mark Carney defended his country's efforts to stop the flow of fentanyl and said Ottawa is strengthening its trade partnerships across the world in response to U.S. President Donald Trump's tariff letter.