All over the world, people are scraping together whatever they have and leaving their homelands, seeking a better life. It has ever been thus. My grandparents and great-grandparents were part of a mass migration from Europe to North America, masses of people hoping to find religious freedom and economic opportunity. In the first half of the 20th Century, millions of African-Americans moved from the southern United States to the north, which might as well have been a different country at the time, creating a sea-change in US history. Indeed, the United States and Canada were both founded by such seekers, first called colonists, then pioneers, later immigrants. (Leaving aside, for the present, the millions who were brought to the US by force, and the millions already there who were massacred or displaced.) Since its founding, the US has never been particularly welcoming to immigrants, each immigrant group, now settled, trying to bar the next one from "their" country. But at va...