The guy dressed in the suit and tie, smiling and shaking a bevy of hands, caught Grayson Thomas’ eye. Grayson wasn’t alone. Teachers and other students at Stevenson Ranch Elementary School couldn’t take their eyes off the lunchtime visitor, either. Grayson, a fifth-grader at the campus near Santa Clarita, Ca., noticed the gentleman’s outward characteristics: Tall and lean. Good looking. Charismatic. Charming. Energetic. Then he made a fatal error: Grayson, 11, pulled a little “made you look” joke on a schoolmate seated next to him, saying something along the lines of “Obama’s visiting our school today,” referring to the magnetic...