Reformist Mexican President Vincente Fox raises eyebrows with his suggestion that over a decade or two Nafta should evolve into something like the European Union, with open borders for not only goods and investment but also people. He can rest assured that there is one voice north of the Rio Grande that supports his vision. To wit, this newspaper.

We annually celebrate the Fourth of July with a paean to immigration, the force that tamed this vast continent and built this great Republic. This is not simply history; immigration...