Former Deputy U.S. Marshal Ed Farrell said Chicago is "absolutely" still a target in the eyes of foreign terrorists.
U.S. airports are on alert after a new call to action from al-Qaida.
The French brothers who began their terror siege this week were acting on orders from al Qaeda, the branch office in Yemen known as al-Qaeda in the Arabian Peninsula.
One of the Paris shooting suspects had al Qaeda weapons training in Yemen, officials say, an area considered to be the brain center of radicalized Muslims that concocted a plan to blow up cargo planes over Chicago in 2010.
Authorities say both attackers in Canada this week were following instructions in a new al Qaeda pocketbook.