President Donald Trump cranked up the pressure on two of America’s key trading partners, Japan and South Korea, firing off letters Monday to the heads of their countries, informing them of their new tariff rate.

Trump delayed the "reciprocal tariffs" in April, vowing to strike roughly 90 trade deals in 90 days. So far, the White House says it has reached trade agreements with only the United Kingdom and Vietnam, as well as a preliminary accord with China.

Trump and his aides have repeatedly shifted their stance on tariffs in the weeks since the president’s “Liberation Day” announcement.