At the heart of the Pew report is its estimate that the number of illegal immigrants in the United States has declined by approximately 900,000 persons. For purposes of this entry, we accept that figure to ask why, exactly, the number of illegal immigrants might have declined.
The Pew report doesn't exactly say. Instead it simply notes that "the analysis does not explain why these changes occurred. During the period covered by the analysis, there have been major shifts in the level of immigration enforcement and in enforcement strategies, as well as large swings in the U.S. economy….But the data in this report do not allow quantification of these factors and are not designed to explain why flows and populations totals declined." (p. iii) Still one of the report's two chief authors, Jeffrey Passel, did say in an interview that, "At this point both of those broad factors seem to be working in the same direction."
Others were less circumspect. The Obama administration immediately claimed credit for its policies in causing the reduction. The only trouble with that is that the administration came into office on January 20, 2009, and the Pew Study immigration numbers covers the period that ends in March 2009, just two months into the Obama presidency. It is questionable to take credit for results that have accrued over a two-year period when you have only been in office the last two months of it.
The safest and most obvious answer to the question is some combination of stiffer enforcement and the effects of the economic downturn. While these two explanations seem plausible, neither is without their potentially undercutting anomalies.
Consider the following from Pew report: "the most marked decline in the population of unauthorized immigrants has been among those who come from Latin American countries other than Mexico." Correspondingly, "the Mexican unauthorized population (which accounts for about 60% of all unauthorized immigrants) peaked in 2007 at 7 million and has since leveled off." (p. i) So the number of illegal immigrants living in the United States, from the country that is the home of origin of 60 percent of the total illegal immigrant population in the United States, has remained stable.
Clearly, the economic downturn and increased enforcement strategies, whatever they might be, have not resulted in a substantial number of that particular population leaving the United States.
Then consider the following. In a 2006 study, the Pew Hispanic Center estimated that almost half of the then estimated 11.5-12 million illegal immigrants in the U.S. came here with visas and stayed after they expired. At a congressional hearing on the subject, a news account reports that a top official with Immigration and Customs Enforcement testified that, "Since 2007, more than 300,000 individuals each year have remained after their visas expire." That number would translate to more than a million new illegal immigrants every four years. These of course are estimates since, as noted, the United States does not have a system in place that would allow officials to check exits against entries.
Still, the Pew study statement "that the most marked decline in the population of unauthorized immigrants has been among those who come from Latin American countries other than Mexico" carries with it the explicit acknowledgment that illegal immigration numbers from visa overstayers have essentially been untouched by either of the two elements that the study mentions as possible reason for the decline – increased enforcement or the deteriorating economy. The study specifically notes that, "The number of unauthorized immigrants from the rest of the world did not change." (p. i)
So clearly, the possible effects of either the economic downturn or increased enforcement did not have a substantial either Mexican immigrants or the estimated "25-40%" of the illegal population made up of visa overstayers. (p. 9 here)
So, to summarize, there has been no discernable decline in the numbers of illegal immigrants from Mexico living in the United States and that group represents 60 percent of the total illegal population. There has been no discernable decline in the number of the illegal visa-overstayer population in the United States that accounts for 25-40 percent of the illegal population.
But there has been a decline in the number of unauthorized immigrants "among those who come from Latin American countries other than Mexico." The decline of illegal immigrants from this group is to be found both in the numbers of such persons entering into the United States and in a decline in the numbers of such immigrants actually living in the United States. Yet, there is no evidence of a documented return home exodus of this group. The report simply says, "return flows to other countries may have increased." (p. iii, emphasis added)
Not so the illegal population from Mexico living in the United States. The report says that "inflows from that county have fallen off sharply in recent years. According to the center's estimates, an average of 150,000 unauthorized immigrants from Mexico arrived annually during the March 2007 to March 2009 period – 70% below the annual average of 500, 000 that prevailed during the first half of the decade." (pp. i-ii)
Yet, that illegal population in the United States has "leveled off" and presumably stabilized at the 7 million figure that Pew's study uses a count of this group. Moreover, for the Mexican origin group there was "no evidence of a recent increase in the number of Mexican-born migrants returning home from the U.S." (p. iii)
The obvious question raised by these data is why, if enforcement or recession, resulted in a downturn in the illegal population living in the United States, that impact was felt only among "those who come from Latin American countries other than Mexico"? Why didn't it affect the visa overstayers? Why are those "who come from Latin American countries other than Mexico" the only group for which there is estimated to be a decline in the number of members actually living in the United States, although there seems to be no direct evidence of a "return flow" of members of that group?
One economist has noted that, "By and large, individuals who remain in the U.S. after their visas expire are more educated than those who cross the border illegally, in part because they must demonstrate proof of completing higher education, having a skilled job or being economically stable." This may help to explain why the recession may not have resulted in a mass exodus home of this group, but doesn't explain why the group of Mexican origin has not done so.
Nor does "increased enforcement" explain why visa overstayers remain, unless you realize that the government has no idea how large this group is or of whom it consists.
Finally, at some point, the economic downturn will end there is no reason to expect that illegal immigration will not reclaim its former numbers, unless in the meantime the United States gets serious about tracking overstayers and making it very difficult for illegal immigrants, whether they cross the border by foot or overstayed their visas.
That is the absolute linchpin to addressing and resolving the issue of illegal immigration into the United States and all of the wrenching and avoidable problems that result from it.