The US steel industry has been the largest beneficiary of special protection from imports for decades, with more than 60 percent of steel imports subject to tariffs at the end of 2017. The average share of all US imports from the world covered by this sort of special protection was only 4 percent as of 2016. Furthermore, special restrictions already cover 94 percent of steel imports from China, which now make up only 3 percent of all US steel imports. On March 8, President Trump announced he is imposing tariffs of 25 percent and 10 percent on all foreign sources of steel and aluminum, respectively—with the exception of Canada and Mexico, as well as possibly others—on the basis that these imports pose a threat to national security.
This PIIE Chart was adapted from Chad P. Bown's blog post, Trump's Steel and Aluminum Tariffs Are Counterproductive. Here Are 5 More Things You Need to Know.