allow us to do this. In the course of working with these data, however, we discovered significant differences between the data that were given to the committee and official (and published and commonly used) data on apprehensions. Although this chapter makes extensive use of official data, their limitations (discussed below) should be kept in mind.
The number of would-be migrants who seek entry to the United States (as to other wealthy destination countries), whether on a temporary or permanent basis, far exceeds the number of visas that Congress has authorized. This gap leads inevitably to unauthorized flows and visa overstays and necessitates an effective immigration enforcement system. Immigration enforcement activities, however, require agents not only to prevent and remove unauthorized immigrants, but also to admit and facilitate legal migration flows for tourism, education, business, and other activities in the United States.
The U.S. immigration system is highly complex. It involves scores of legal visa categories, dozens of grounds for removal, and various opportunities for unauthorized immigrants to seek discretionary relief from enforcement actions in administrative and judicial forums. At most points in the enforcement system, moreover, agency personnel and officials can exercise discretion in the use of their authority.
Today’s immigration enforcement system reflects important policy innovations, decisions, institutional changes, and political events that have developed over almost one-half century, dating back to the Immigration and Nationality Act of 1965, which ushered in the modern era of immigration law and policy. Appendix A provides a timeline of the post- 1965 statutory, policy, and administrative changes that are most relevant to current enforcement challenges and to the budget-relevant interactions between DOJ and (since 2003) DHS. More recently, the aftermath of the events of 9/11 and their interaction with changes in the 1996 immigration law have been of overarching importance in understanding today’s immigration policy and operational landscape.
Because the 9/11 hijackers had entered the country with properly issued visas, immigration issues became irrevocably linked with antiterrorism and national security. The calls for secure borders were widespread and urgent, and immigration enforcement became understood as a front-line measure that had to be strengthened to protect the country. Thus, immigration functions were largely incorporated in the new cabinet agency, DHS, border-related resources grew dramatically, and the interoperability of federal databases—including data collected and managed by immigration agencies—became broadly available for immigra-