He is correct that migration from Mexico has accelerated since NAFTA took effect in 1994, but it's a stretch to attribute that to the trade agreement.
Independent analysis suggests there are several other factors involved besides NAFTA.
Experts point out that migration from Mexico in the 1990s was encouraged by the booming economy in the United States. Migration peaked in 2000 and since then has fallen off by more than a quarter following the slowdown in the economy after 2001.
Emigration was already high before 1994, especially due to people fleeing the wars in Central America in the 1980s. Poverty, coupled with natural disasters (Hurricane Mitch in Honduras in 1998 and an earthquake in El Salvador in 2001) continues to draw large numbers of migrants from Central America.
In fact, immigration patterns were not substantially affected by NAFTA, according to a February 2004 report by the Congressional Research Service.
The report found that while legal and unauthorized worker migration from Mexico to the United States did accelerate after NAFTA was implemented in 1994, the trade agreement was "largely irrelevant."
It found that workers were drawn to the United States by Mexico's inability to provide jobs for a burgeoning work force, as well as periodic financial crises that caused huge job losses and undermined confidence in the Mexican economy.