Trump uses tariffs as a key tool to force changes to U.S. trade relationships, but his on-again-off-again approach has roiled markets and stoked uncertainty.

President Donald Trump is spamming world leaders with letters threatening massive tariff hikes if they don’t strike trade deals with Washington as the U.S. blows past its own 90-day deadline for deals with 90 countries. As the letters multiply, it turns out they are partially copied and pasted.