Illegal immigrants captured on U.S. borders down 23 times in nine months . Officials believe enforcement has deterrent effect on illegal immigration . Outside economic , political and social factors also are `` always involved '' in fluctuating levels of immigrants seeking entry into the United States , he said . Official : Movement of National Guard troops along Southwest border may be a factor .
Illegal immigrants captured on U.S. borders down 23 times in nine months . Officials believe enforcement has deterrent effect on illegal immigration . Official : Movement of National Guard troops along Southwest border may be a factor .