I was in Minnesota today speaking about counterterrorism and homeland security at a forum organized by Minnesota Public Radio and the William Mitchell College of Law. The site was the Mall of America, the gargantuan combination of shopping center and amusement park on the outskirts of the Twin Cities. Step outside the auditorium where the event was held and you are standing next to a roller coaster. One of the themes voiced by our panel, which also included Eric Schmitt of the New York Times and Juliette Kayyem of Harvard University, was the continuing possibility of prospective terrorists, including American “lone wolves,” taking advantage of the inherent vulnerability of many open public spaces in the United States. Another theme was the difficulty in cultivating public understanding of terrorism in a way that accepts prudent precaution while avoiding overreaction to whatever terrorist incidents do occur. A reflection of some of the issues raised by both themes was a question from one member of the audience: “Why did we get searched when we came in here?”—referring to a search of bags when entering the auditorium, not the mall.

We should not be surprised if more individuals who decide to turn to indiscriminate violence, perhaps taking a page from the book of the “D.C.sniper” who terrorized the Washington area a few years ago, exploit the openness of those public spaces. The reason for such a turn could be anything, but most likely it would be the anger over U.S. policies abroad that was the chief motivation of other cases of American-bred terrorists over the past three years. We cannot track or trace most of the individuals who would do that because they have not yet turned to violence and we thus do not know who they are. The public spaces cannot operate in the intended way if they are not kept open. Shopping malls present prime terrorist opportunities, especially during seasons when they are especially crowded. The Mall of America, as one of the best known malls in the country, has been mentioned by foreign terrorists as a possible target and would not have escaped the notice of American lone wolves.

After our event I had the opportunity to talk with some of the mall's security staff. Their operation is big, as befitting a big and famous mall. They use sophisticated techniques for trying to spot sources of trouble early while minimizing disruption to the patrons' shopping and entertainment experiences. Based on what I heard, they are probably doing about as good a job as can be expected in making the facility they are charged with protecting as safe as possible. But with the unavoidable openness, they can only do so much. I will not be surprised if their protectee someday becomes too inviting a target for someone.