Financial markets, which have shown increasing insensitivity to tariff threats from the US, will face a test at the Monday open after President Donald Trump declared a 30% rate for the European Union and Mexico effective Aug.

Investors have so far behaved as if they’re counting on the U.S. president to back down, having seen previous U-turns from his administration.

President Donald Trump has posted two new letters on his social media platform announcing tariffs on the European Union and Mexico.

President Donald Trump posted letters to the leaders of Mexico and the European Union, saying they had not done enough to head off the new tariffs.

Major stock indexes were slightly lower on Friday as U.S. President Donald Trump's announcement of tariffs on imports from Canada fanned worries about trade tensions, with the Canadian dollar down against the greenback.

President Trump said he plans to impose blanket levies of 15% to 20% on most trading partners that haven't yet received suggested tariff rates. That would be higher than the 10% baseline currently in effect.

It shows that personal grudges rather than simple economics are a driving force in the U.S. leader’s use of tariffs.