When Mitt Romney said in a Republican debate that illegal immigrants could be encouraged to self-deport, the smart people all laughed at him. But the latest Pew Hispanic Center report suggests that this may, in part, be happening. Consider:

• In the five-year period from 2005 to 2010, about 1.4 million Mexicans immigrated to the United States and about 1.4 million Mexican immigrants and their U.S.-born children moved from the United States to Mexico.
• In the five-year period a decade earlier (1995 to 2000), about 3 million Mexicans had immigrated to the U.S. and fewer than 700,000 Mexicans and their U.S. born-children had moved from the U.S. to Mexico.
• This sharp downward trend in net migration has led to the first significant decrease in at least two decades in the number of unauthorized Mexican immigrants living in the U.S.—to 6.1 million in 2011, down from a peak of nearly 7 million in 2007. Over the same period the number of authorized Mexican immigrants rose modestly, from 5.6 million in 2007 to 5.8 million in 2011.

Much of this has to do with relative economic conditions in the United States and Mexico. But immigration enforcement is also playing a role.

• Apprehensions of Mexicans trying to cross the border illegally have plummeted by more than 70% in recent years, from more than 1 million in 2005 to 286,000 in 2011—a likely indication that fewer unauthorized immigrants are trying to cross. This decline has occurred at a time when funding in the U.S. for border enforcement—including more agents and more fencing—has risen sharply.
• As apprehensions at the border have declined, deportations of unauthorized Mexican immigrants—some of them picked up at work or after being arrested for other criminal violations—have risen to record levels. In 2010, nearly 400,000 unauthorized immigrants—73% of them Mexicans—were deported by U.S. authorities.
• Although most unauthorized Mexican immigrants sent home by U.S. authorities say they plan to try to return, a growing share say they will not try to come back to the U.S. According to a survey by Mexican authorities of repatriated immigrants, 20% of labor migrants in 2010 said they would not return, compared with just 7% in 2005.

National Journal has an interesting take on what this could mean for the conventional wisdom about the Hispanic vote, long assumed to be a harbinger of Democratic dominance, going forward.