Currently, about 90 percent of aluminum used in American manufacturing is imported as well as one-third of steel. But he showed more leniency than initially thought.
"A strong steel and aluminum industry are vital to our national security, absolutely vital", he said. At Thursday's announcement, Trump was joined by US workers from the affected industries - but not GOP congressional leaders.
Trump confirms there will be exemptions on his new steel tariffs for some countries, and singles out Australia as a likely beneficiary.
"I have a feeling we'll make a deal on NAFTA", Trump said.
President Donald Trump indicated on Thursday that he was willing to exclude some countries from the steel and aluminum tariffs for national security reasons.
Government and companies are already lining up for a break.
The European Union has already identified US blue jeans, bourbon, and motorcycles as possible targets.
He further suggested that the president consider: enacting a global tariff of at least 24 percent on all steel imports from all countries; instituting a tariff of at least 53 percent on all steel imports from 12 counties with a quota, or setting a quota on all steel products from all countries equal to 63 percent of 2017 exports to the U.S.
Trump's belittling of allies is unworthy of a USA president
Likewise, Trump's invitation to countries to plead their case for being exempted from the tariffs might prove a tough sell. Moreover, there is a risk, albeit slight, that imposing tariffs could set off a beggar-thy-neighbor trade war.
Japan's Minister of Economy, Trade and Industry Hiroshige Seko arrives at the European Commission headquarters ahead of a meeting with European Trade Commissioner Cecilia Malmstrom and U.S. Trade Representative Robert Lighthizer, to discuss steel overcapacity, in Brussels, Belgium March 10, 2018.
Worsening trade ties will test China's policy of "strategic composure" in dealing with Mr Trump's America First ethos.
More than 100 House GOP lawmakers sent a letter to the president Wednesday urging him to "reconsider the idea of broad tariffs to avoid unintended negative consequences to the USA economy and its workers".
Trump said the "aggressive" foreign trade amounted to an "assault" on the United States, but that he would also show flexibility with friendly countries, possibly removing tariffs for some. Trading partners including the European Union threatened retaliation, triggering fears of a trade war. The group also warned that retaliatory tariffs from other countries could drive up the price of other USA goods, as well.
China was quick to respond to Trump's announcement. Europe would also take measures to limit eventual excess of imported steel and aluminium into Europe in line with World Trade Organisation (WTO) rules while filing a complaint before the WTO, he added. All countries with a security relationship with the USA will be invited to attempt to negotiate individual exclusions from the tariffs.
Several major trading partners have said they will respond to the tariffs with direct action.
Canadian Foreign Minister Chrystia Freeland told reporters in Toronto that NAFTA is "a completely separate issue".
Japan's foreign ministry said the tariffs risk having a large effect on economic and cooperative relations with the US government.
The Japan Aluminium Association also said the US decision to impose tariffs is "not in accordance with global trade rules" and is "extremely regrettable".