In the case of the alleged plot against the JFK airport, how much planning and actual likelihood of success are required to prosecute someone? If this were anything but terrorism (say, a plot to steal your potted plants,) would courts even hear a case in which nothing happened, or would they dismiss it with prejudice, complaining that, so far, the authorities have purposefully arrested innocent (though possibly ill-intentioned) people? (After all, they were arrested on purpose, knowing full well they hadn't hurt anyone yet.) Fine lines.