From the 'Is Not Evidence of Absence' Dept.
Comes this story:
SASABE, Mexico, Nov. 3 ? A crackdown along the U.S.-Mexico border designed to prevent terrorists from entering the United States hasn't stopped even one known militant from slipping into America since Sept. 11, an Associated Press investigation has found.
It's a long article with much gray area; I'd caution reading it before jumping to conclusions. (Via Virginia Postrel)