SEOUL — For corporate Japan, America’s treatment of its steel industry has been one blow after another. First, there were the objections to Nippon Steel’s takeover of its U.S. rival ...

US President Donald Trump says the government has a golden share in US Steel that he described as under his control. Such a stake could let the president veto some decisions by Japanese firm Nippon Steel after its planned takeover of the American steelmaker.

For Japan and many other countries, the vulnerability that comes with relying on U.S. markets has become startlingly clear. First came tariffs on Canada, China, and Mexico. Then, in February, the administration introduced a 25 percent tariff on steel and aluminum (this week,