November 2017: the White House imposed 20 percent tariffs on imported Canadian lumber March 2018: 25 percent tariff on steel and 10 percent tariff on aluminum go into effect with exemptions for selected countries July: US tariffs on $34 billion of Chinese imports go into effect August: US imposes tariffs on $16 billion of imports from China September: US tariffs on $200 billion of Chinese imports take effect Source: Peterson Institute for International Economics, https://piie.com/system/files/documents/trump-trade-war-timeline.pdf