As Congress debates comprehensive immigration reform and its component parts of immigration control (i.e., border security and interior enforcement), legal reform (i.e., temporary and permanent admissions), and the resolution of unauthorized alien residents, concerns arise over the capacity of the Department of Homeland Security (DHS) to identify and remove temporary aliens on nonimmigrant visas who fail to depart after their visas expire. It is estimated that each year hundreds of thousands of foreign nationals overstay their nonimmigrant visas or enter the country illegally (with fraudulent documents or bypassing immigration inspections). The most recent estimate (published in 2013) is that 11.7 million foreign nationals resided in the United States without authorization in 2012.
DHS does not have reliable data on emigration and nonimmigrant departures from the United States. As a consequence, reliable estimates of the number of nonimmigrant overstays are not available. Over the years, the overstay estimates ranged from 31 percent to 57 percent of the unauthorized population (depending on methodology). A 2013 study of visa overstays from 2000 to 2009 estimated that total nonimmigrant overstays to the United States dropped from 705,000 per year to 190,000 per year, or about 73%, over the decade. As of June 2013, the U.S. Government Accountability Office (GAO) reported that DHS's unmatched arrival-departure records totaled more than 1 million; however, the failure of DHS to consistently update the alien's record—for example, if the authorized period of admission is extended, if deferred departure is granted, or if the immigration status changes—is a major factor that prevents DHS from calculating reliable estimates of overstays.