Columbia subject headings:
Border patrols--United States.
Border security--United States.
Illegal aliens--Government policy--United States.
Intelligence service--United States.
Terrorists--Travel--United States--Prevention.
Harvard subject headings:
Border patrols--United States
Border security--United States
Illegal immigration--Government policy--United States.
Intelligence service--United States
Noncitizens--Government policy--United States
Terrorists--Travel--United States--Prevention.
Princeton subject headings:
Border patrols--United States.
Border security--United States.
Illegal aliens--Government policy--United States.
Intelligence service--United States.
Terrorists--Travel--United States--Prevention.