"When the border was relatively porous, migrant workers would come and go with the season. Yet when US authorities began cracking down, Mexican migrant workers would stay in California (or Texas) because, “I’m not risking that again.” Thus paradoxically, efforts to keep out “illegals” may lead to an increase in the resident migrant worker population in the United States. Again, this shouldn’t surprise a libertarian reader; this type of outcome happens all the time when the federal government tries to “fix” a perceived social problem."