And on the American left there is something like revulsion at the idea of the "beautiful wall" President Trump intends to build along the 1,900-mile border between the U.S. and Mexico.

The opposition's arguments are usually rooted in economics or practicality. The wall is unnecessary. It will not stop people from coming illegally. It costs too much.

Yet something deeper is afoot here. The idea of a permanent barrier between our countries goes to the heart of the divide between our two Americas on the most fundamental of questions.

Who are we? What is a nation? What does America stand for?

Those desperate to see the wall built, illegal immigration halted, and those here illegally deported, see the country they grew up in as dying, disappearing, with something strange and foreign taking its place.