President Trump loves walls—besides a border wall with Mexico, he wants to erect trade walls to protect American steel and aluminum with tariffs of 25 and 10 percent, respectively.

In his famous poem about walls, Robert Frost said, “Something there is that doesn’t love a wall,” adding that before he built one, “I’d ask to know what I was walling in or walling out, and to whom I was likely to give offence.” Those are good questions for Mr. Trump’s policy.

He wants to wall out foreign products that are cheaper than American products. But this will trouble not only nations that produce them, but also American consumers who like to save money.  

There’s also a question of constitutionality, since the president’s power to do this is based on national security. And the biggest question:  will tariff walls even work in a global economy?

Many important questions about walls.