All across Mexico’s ruddy central plains, most of the people who could go north already have. In a region long regarded as a bellwether of illegal immigration — where the flow of migrants has often seemed never-ending — the streets are wind-whipped and silent. Homes await returning families, while dozens of schools have closed because of a lack of students. …

As Congress considers a sweeping overhaul of immigration, many lawmakers say they are deeply concerned that providing a pathway to citizenship for the estimated 11 million immigrants living illegally in the United States would mean only more illegal immigration. …

But past 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. Long-running surveys of migrants from Mexico found that work, not the potential to gain legal status, was the main cause of increased border crossings in the 1990s and 2000s. And as Mr. Saldivar points out, times have changed.

The American economy is no longer flush with jobs. The border is more secure than ever. And in Mexico the birthrate has fallen precipitously, while the people who left years ago have already sent their immediate relatives across, or started American families of their own.