Long-threatened tariffs from U.S. President Donald Trump have plunged the country into a trade war abroad — all while on-again, off-again new levies continue to escalate uncertainty.

Trump has praised tariffs as a fix for economic issues, but their erratic rollout and shifting reasons have worried investors. See a timeline of the president’s trade rhetoric.

U.S. President Donald Trump has made numerous tariff threats since returning to office on January 20, ranging from a universal duty on imports to targeted tariffs on specific sectors or countries, in a bid to get others to meet his policy demands.