In recent years, unusually elevated numbers of migrants from countries of special interest reaching the U.S.-Mexico border have been found to match U.S. terrorism “watch lists” — the Terrorist Identities Datamart Environment (TIDE), or the Terrorist Screening Database (TSDB). Such migrants are known as “special interest aliens” (SIAs). These are aliens with citizenship in some 30 countries of concern in the Middle East, South Asia, and northern Africa where terrorist organizations are known to operate and extremist ideologies are ubiquitous. While no attack on U.S. soil is attributed to SIAs who crossed the southern border, the number encountered there or en route who were found to have matched TIDE or TSDB records has risen drastically from 2012 to exceed 100 by 2017, according to information provided to the Center for Immigration Studies. A number of these were regarded as significant security risks that prompted security investigations.