After some back and forth over whether today would be the day, President Donald Trump said that we would impose global tariffs on steel and aluminum imports into the United States.

Reports indicated that White House staffers and Congressional Republicans were trying to dissuade Trump from the move and to postpone today’s expected announcement. But the president apparently had other ideas and he made the announcement during a previously-scheduled meeting with steel and aluminum executives.

The president announced his rationale for the policy in a tweet:

Our Steel and Aluminum industries (and many others) have been decimated by decades of unfair trade and bad policy with countries from around the world. We must not let our country, companies and workers be taken advantage of any longer. We want free, fair and SMART TRADE!

— Donald J. Trump (@realDonaldTrump) March 1, 2018

Trump later acknowledged that in effect he was starting a trade war and that trade wars are good and easy to win:

When a country (USA) is losing many billions of dollars on trade with virtually every country it does business with, trade wars are good, and easy to win. Example, when we are down $100 billion with a certain country and they get cute, don’t trade anymore-we win big. It’s easy!

— Donald J. Trump (@realDonaldTrump) March 2, 2018

Trump said at a White House meeting that he has opted to impose a 25-percent tariff on steel and 10 percent on aluminum, higher than one of the recommendations contained in recently-released Commerce Department reports, which supported a 24.4-percent tariff on steel and 7.7 percent on aluminum.

The Commerce Department released reports in mid-February after ten months of work which found that steel and aluminum were important to national security and outlining several options the president could choose from to impose tariffs and/or quotas on imports. All of the options would have covered all imports into the US of steel and aluminum. The Commerce investigation was undertaken under Section 232 of the Trade Expansion Act of 1962, which authorizes the US government to examine the harmful effects of imports on strategic industries that are deemed essential to national security and to impose trade restrictions on imports.

The domestic industries, especially steel producers, welcome this development, but manufacturers that consume steel and aluminum are concerned about the consequences of import tariffs. Roy Hardy, president of the Precision Metalforming Association, said that imposing steep tariffs on steel “would devastate downstream U.S. steel consuming manufacturers.” “If these tariffs are imposed,” he added, “the US will become an island of high steel prices.”

American jobs are also at risk: The last time the US imposed steel tariffs, in 2002, more than 200,000 were lost.

Another concern is that other countries will retaliate. The sector most likely to face retaliation is agriculture, and the American Soybean Association (ASA) has noted especially the potential for retaliation by China, which purchases one-third of the soybeans grown in the US at a value of more than $14 billion. The Chinese have already identified US soybeans as a target for retaliation in response to the Commerce Department report.

The US Aluminum Association wanted the administration to address Chinese overcapacity, while avoiding unintended consequences for US production and jobs. “Of particular note,” the organization said in a statement, “the North American aluminum industry has a long-term, essential trading relationship with Canada, which supports U.S. jobs and industry growth. By statute, Canada is considered part of the nation’s defense industrial base.”

The stock market apparently has reservations about the Trump tariffs: the Dow Jones Industrial Average dropped 500 points on the news.

Dean A. Pinkert, an attorney at Hughes Hubbard and the former Commissioner of the US International Trade Commission noted that overcapacity in the steel and aluminum industries a serious problem, “largely the result of Chinese policy decisions.”  “The Trump administration appears to have chosen an unconventional approach to the problem by relying on a national security justification for the imposition of trade relief,” he added. “The details, however, will be very significant and have yet to be released.”