Canada, China and the European Union have already said they would respond with tariffs of their own that could lead to billions of dollars in American export losses. Those levies would harm the farmers and business interests that the Trump administration has promised to protect and would fuel a trade fight that could undermine the president’s goal of strengthening American industry.

Li Xinchuang, the vice chairman of the China Iron and Steel Association, called the president’s move “stupid,” saying, “Trump’s decision does no good to everyone except a few American steel enterprises.”

And John M. Weekes, Canada’s negotiator for the North American Free Trade Agreement in the early 1990s, said the president’s “notion is going down very badly in Canada.”

“It certainly will have a negative effect on our bilateral relationship,” he said.