The worst part of Trump's steel and aluminum tariffs is that they could cross a line no one's crosse

Proposed tariffs on steel and aluminum could not only hurt America's allies and rivals alike, they could violate a trust the world's trading partners have kept since World War II. The Trump administration's invocation of national security sets a dangerous precedent, especially when it comes to China. Countries would have the right to retaliate in equal measure in other industries if these tariffs are enacted, and the result could be a trade war. If President Trump puts in place steel...