Business groups, economists and even some Republicans cautioned that new tariffs on goods from Canada, Mexico and China could undercut U.S. industry and the economy.
Shares in Japanese and South Korean manufacturers tumbled on concern that tariffs will hurt trade in North America, where they have major investments in factories.
Amid warnings of price increases, Canada moved quickly to retaliate, China said it had planned countermeasures, and Mexico said it would soon unveil its response.