Ward might be right,  at least an explosive or vehicle borne threat. It does not have to be terrorist motivated  act. Somebody  taking a car into the capital could happen. It happened at two airports in Hawaii,  pissed off  guy drove his jeep into Kahului Airport  then set it on fire. The other,     
as pissed off  kid drove his car into  Aloha Airlines  baggage claim,  then to  Hawaiian baggage claim. Airport Sheriff's classified case as  an  accident. Should have been reckless endangering, guy was  pissed at  his girlfriend. No  accident when you drive into the ground level elevator area, make left turn, spin around then  go to  the Hawaiian side.