U.S. President Donald Trump has a chance to pursue protectionist trade measures that could be his most significant trade restrictions yet. After an investigation launched in April 2017, the Commerce Department has found that steel and aluminum imports threaten to impair U.S. national security. To counter that threat, it has recommended a wide range of remedies, including a global tariff on steel imports of at least 24 percent and quotas restricting imports to just 63 percent of their 2017 volume. Trump and his administration now have until April 11 and 19 to decide what measures to take on steel and aluminum imports, respectively....