These guys are sending a message that absolutely no-one is safe anywhere.
They'll kill you when you're washing the car, pumping gas, mowing the lawn, waiting for the bus, going to school, shopping at Michael's, absolutely anywhere. They're trying to be totally unpredictable.
You can't protect yourself by not flying, staying out of federal buildings, nightclubs, etc.. There's nothing you can do. Any moment anywhere you may be shot to death.
That's the definition of terror.
Sure there is. We can turn Mecca into a radioactive parking lot, right after we steal their holy meteorite.