Mark Bernstein profiles Douglas Massey, the founder and co-director of Princeton's Mexican Migration Project—"a unique database," Bernstein writes, "of ethnographic information about border crossing: who migrates, where they come from, where they go, and how that has changed over time." From that data, Massey concludes that

• We are not being flooded with illegal Mexican migrants. The total number of migrants from Mexico has varied very little since the 1950s. The massive influx many have written about never happened.

• Net illegal migration has stopped almost completely.

• Illegal migration has not stopped because of stricter border enforcement, which Massey characterizes as a waste of money at best and counterproductive at worst.

• There are indeed more undocumented Mexicans living in the United States than there were 20 years ago, but that is because fewer migrants are returning home -- not because more are sneaking into the country.

• And the reason that fewer Mexican citizens are returning home is because we have stepped up border enforcement so dramatically.

Mull over that last point for a minute. If Congress had done nothing to secure the border over the last two decades -- if it had just left the border alone — there might be as many as 2 million fewer Mexicans living in the United States today, Massey believes.

Here's why:

What heightened border enforcement did, Massey says, was shift the problem. Unable to cross where they traditionally had -- into California and Texas -- Mexican migrants instead found new places to cross, particularly making the dangerous Sonoran Desert crossing into Arizona. If they succeeded, they then moved on to other states. Arizonans who complained during the 1990s and early 2000s about a surge in illegal migration were not imagining things. But it was the American government, Massey says, that unwittingly had channeled the flow of migrants into their backyard.

Mexicans had been crossing the Rio Grande ever since it was a border, but migration traditionally was seasonal and cyclical. Young men would head to El Norte in search of agricultural or construction work, earn money, and then return home. But when it became too risky and too expensive to migrate seasonally, migrants simply chose to stay in the United States. Because they no longer were returning home regularly, they could look for work farther from the border. They also settled down and had families, which made them even less likely to leave.

While the recession has essentially ended net illegal immigration into the United States, legal migration has picked up: "In 2010, the most recent year for which statistics are available, a record 516,000 Mexican citizens entered the United States with legal visas." I'm glad to hear that the feds are granting visas to more people. I'd be gladder if the same government weren't simultaneously engaged in a harsh and pointless crackdown on border-crossers.

Elsewhere in Reason: Massey is cited frequently in our pages.