Homegrown terrorist Jeffrey Leon Battle considered America the “land of the kaffirs,” or unbelievers, and the American people “pigs.” He once lamented to an acquaintance—who happened to be a government informant—that the Sept. 11, 2001, terrorist attacks did not sufficiently damage the U.S. economy. “This is the land of the enemy,” he said of his own country in a May 8, 2002, conversation secretly recorded by the government. He explained to a friend how his “burning desire” to become an Islamic martyr had inspired his aborted quest to join forces with al Qaeda in Afghanistan, where he could kill American...