Trump administration consults unused 1930s law for tariff playbook

The Trump administration keeps finding new ways to wage trade wars. As one novel tariff authority nears its expiration, it's testing another — threatening huge duties on Canadian goods under a never-before-used law. Why it matters: The administration's willingness to test new trade authorities makes tariff policy harder for businesses, investors and foreign governments to handicap. It's hard to know which will survive challenges in the courts, and over what time horizon there may be any…