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.

The Trump administration has again delayed the date when new reciprocal tariffs will go into effect, and the president threatened a 35 percent tariff on Canada.