"The Immigration and Nationality Act (INA) spells out a strict set of admissions criteria and exclusion rules for all foreign nationals, whether coming permanently as immigrants (i.e., legal permanent residents) or temporarily as nonimmigrants. Notably, any alien who has engaged in or incited terrorist activity, is reasonably believed to be carrying out a terrorist activity, or is a representative or member of a designated foreign terrorist organization is inadmissible. After the September 11, 2001 terrorist attacks, the INA was broadened to deny entry to representatives of groups that endorse terrorism, prominent individuals who endorse terrorism, and spouses and children of aliens who are removable on terrorism grounds (on the basis of activities occurring within the previous five years). The INA also contains grounds for inadmissibility based on foreign policy concerns. Provisions of the REAL ID Act (P.L. 109-13, Division B), enacted on May 11, 2005, further expand the terror-related grounds for inadmissiblity and deportation. 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 September 11, 2001, and as a result, opportunities to intercept the September 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."
CRS Report for Congress, RL32564