Be it Europe, Canada or Asia, other countries said they would respond to Mr. Trump’s steel and aluminum tariffs with restrictions of their own.
“It certainly will have a negative effect on our bilateral relationship,” he said.
American businesses are more tied to the global economy than ever before, and the Trump administration is seeking concessions from trading partners to put American companies on a more competitive footing. Negotiators from Canada, Mexico and the United States were meeting in Mexico City to hash out changes to Nafta, and Washington is trying to revise a trade deal with South Korea. The possibility of tariffs complicates both efforts.
Mr. Trump appeared unmoved by the blowback, posting a series of Twitter messages on Friday defending his proposal to impose tariffs of 25 percent on steel and 10 percent on aluminum.
“We must protect our country and our workers. Our steel industry is in bad shape. IF YOU DON’T HAVE STEEL, YOU DON’T HAVE A COUNTRY!” Mr. Trump tweeted.
Yet the United States does not control the global economy, and the tariffs, which Mr. Trump is expected to sign next week, could incite other countries to challenge it at the World Trade Organization. If the organization rules against the United States, that will test the Trump administration’s willingness to follow global trade rules.
The tariffs rest on a little-used legal provision that allows Mr. Trump to restrict imports to try to bolster the American industrial base in the interest of national security. That power will face scrutiny by the World Trade Organization but, perhaps more significant, could prompt other countries to follow suit in using national security as a reason to wall off their markets.
American technology companies, agricultural producers and other industries could ultimately lose business abroad as nations seek to erect similar barriers.
Robert L. Shanks, Ford Motor’s chief financial officer, said commodities markets had already started to price in increases for steel and aluminum on the expectation that Mr. Trump would impose the tariffs. The effect on Ford, he said, is “not positive” given the automaker uses those metals in the cars they produce.
The European Union detailed a three-step plan to penalize $3.5 billion of American trade — the same amount of European steel and aluminum the bloc estimates would be harmed by the planned tariffs. It proposed taxing American exports including bourbon, bluejeans, orange juice, cranberries, rice and motorcycles. The European Union could then take action to protect their own metal makers from a surge in imports, and bring a case against the United States at the World Trade Organization.
A European Union official said that the bloc had been preparing for the announcement for months and that everything was in place for a swift, proportionate response.
The measures were intended to put pressure on politically sensitive areas, trade analysts said. Harley-Davidson motorcycles are made in the home district of Speaker Paul D. Ryan, Republican of Wisconsin. Orange juice comes from the swing state of Florida. Restrictions on Kentucky bourbon could add pressure on the Senate majority leader, Mitch McConnell, who is from the state.
Retaliation could hit hardest in many of the rural communities that were strongholds for Mr. Trump. Farmers are among America’s largest exporters, and often become a target in trade spats, said Darci Vetter, the former chief agricultural negotiator for the United States trade representative. She said the agricultural community was “rightly nervous” about the prospect.
Canada and Mexico were America’s No. 1 and No. 3 largest agricultural markets in 2016, and South Korea is a major market for beef, corn, pork and fresh fruit, Ms. Vetter said. The United States exports cotton to Turkey and wheat and dairy to Brazil, other major suppliers of steel.
Senator John Cornyn of Texas expressed concern on Friday that America’s trading partners might respond by imposing tariffs on agriculture, which he said would “devastate our agricultural communities.”
Other countries have been less specific, but no less emphatic, in their threats. Canada’s minister of foreign affairs, Chrystia Freeland, said that Canada stood ready to defend its trade interests, while the Australian trade minister, Steven Ciobo, said the tariffs would set off retaliatory measures that would hurt everyone.
American steel companies are a key constituency for Mr. Trump, who won the support of some blue-collar workers by pledging to revive United States industry. The steel industry has shed hundreds of thousands of jobs in the country in the past two decades, partly because of automation and partly because of a flood of production from China, which has driven down global prices to a level where some American mills cannot compete.
American steel and aluminum companies were the loudest in applauding the president’s efforts to help their industries. Labor unions and Rust Belt politicians, including Democrats, commended Mr. Trump for fulfilling an important political promise he made during the campaign.
“Our view is we needed some relief on illegally trade products,” said John J. Ferriola, chairman, president and chief executive of Nucor Corporation. “Whatever the remedy, it had to be comprehensive trade relief.”
On Fox Business Network Friday morning, Peter Navarro, a top White House trade adviser, said he did not believe any country would retaliate, “for the simple reason that we are the most lucrative and biggest market in the world.”
“They know they’re cheating us, and all we’re doing is standing up for ourselves,” he added.
Mr. Trump’s announcement on Thursday was a clear signal to many observers that the pro-trade advisers in the Trump administration — who have tried to stay the president’s hand on tariffs and withdrawing from trade agreements — might have less influence than they believe. That could further fuel trade tensions and make it less likely that the United States will be able to reach the types of bilateral or multilateral agreements that have helped expand American exports.
Antonio Ortiz-Mena, a senior adviser at the Albright Stonebridge Group, said that if the United States was willing to impose penalties like these on its close trading partners, other countries would be less eager to negotiate trade deals with the United States.
