President Donald Trump still wants to build a wall along the southern border with Mexico. At times, he’s nearly taken a first step toward that goal, most recently during bipartisan negotiations over immigration. Democrats in Congress offered to fund a border wall in exchange for protections for immigrants living in the U.S., but the deal collapsed without the president’s support.

On Thursday, Trump shocked the world by unilaterally announcing tariffs on steel and aluminum. In the name of national…