The Immigration and Nationality Act (INA) spells out a strict set of admissions criteria and exclusion rules for all foreign nationals who come permanently to the United States as immigrants (i.e., legal permanent residents) or temporarily as nonimmigrants. Notably, any alien who engages in terrorist activity, or is a representative or member of a designated foreign terrorist organization, is generally inadmissible. After the Sept. 11, 2001, terrorist attacks, the INA was broadened to deny entry to representatives of groups that endorse terrorism, prominent individuals who endorse terrorism, and (in certain circumstances) the spouses and children of aliens who are removable on terrorism grounds. The INA also contains grounds for inadmissibility based on foreign policy concerns.
The report of the National Commission on Terrorist Attacks Upon the United States (also known as the 9/11 Commission) concluded that the key officials responsible for determining alien admissions (consular officers abroad and immigration inspectors in the United States) were not considered full partners in counterterrorism efforts prior to Sept. 11, 2001, and as a result, opportunities to intercept the Sep. 11 terrorists were missed. The 9/11 Commission's monograph, 9/11 and Terrorist Travel, underscored the importance of the border security functions of immigration law and policy.