Global markets did not like Trump's Mexico tariff tweet

By the numbers:

• The Mexican peso fell almost 2% against the dollar to its lowest value since early March.
• Yields on the 2-year U.S. Treasury note dropped below 2% for the first time since February 2018, and to the lowest since September 2017 on the benchmark 10-year note.
• S&P 500 futures were lower by 1.2%, London's FTSE 100 fell more than 1%.
• Chinese shares were slightly lower, falling by around 0.2%. Germany's DAX was off by more than 1.5%.
• Shares of Ford lost 4% in pre-market trade. GM dropped more than 5%.

Be smart: "Imposing these tariffs is in principle, not allowed under the free trade agreement currently in place between Mexico and the United States or under WTO general frameworks," wrote Tania Escobedo, strategist at RBC Capital Markets.

• "It is likely, however, that Trump will claim the measure is a matter of national security, referring to the International Emergency Economic Powers Act (IEEPA)."

Go deeper: Trump's Mexico tariffs could decimate the auto industry