The Chicago studios of talk-show superstar Oprah Winfrey and the iconic “Sears Tower” (renamed Willis Tower) were the targets of a terrorist truck-bomb plot in 2009. But initially unbeknownst to federal authorities, two of the conspirators recently were arrested for unrelated state crimes in different parts of the country. The alleged bombers targeted Ms. Winfrey’s Harpo Studios because they resented her popularity and power, while the tower was selected because of its obvious landmark status. The bomb plot itself, planned in 2009, was inspired by militant Islamist hatred of American military involvement in Afghanistan and Iraq, according to law...