Columbia subject headings:
Aliens--United States--Identification.
Illegal aliens--United States.
National security--United States.
Terrorism--United States--Prevention.
United States--Emigration and immigration--Government policy.
Visas--United States.
Harvard subject headings:
Illegal immigration--United States.
National security--United States
Noncitizens--United States
Noncitizens--United States--Identification
Terrorism--United States--Prevention
United States--Emigration and immigration--Government policy
Visas--United States
Princeton subject headings:
Illegal aliens--United States.
National security--United States.
Noncitizens--United States--Identification.
Terrorism--United States--Prevention.
United States--Emigration and immigration--Government policy.
Visas--United States.