One argument often heard in the debate over comprehensive immigration reform is that the flow of illegal immigrants from Mexico to the United States, once measured in the hundreds of thousands per year, has slowed dramatically and is not likely to pick up again.

“All across Mexico’s ruddy central plains, most of the people who could go north already have,” reported the New York Times in early April. “[P]ast experience and current trends in both Mexico and the United States suggest that legalization would not lead to a sudden flood of illegal immigration on the scale of what occurred after 1986.”