Dr. Stern was 15 when his parents sent him by himself to live with an uncle in the United States. They hoped to join him, and to bring their two younger children. But the “golden door was not wide open,” Dr. Stern later said, describing the reception that awaited many refugees during World War II. When Hitler came to power in Germany in 1933, Guy Stern’s father grasped the danger that awaited Jewish families like theirs and offered his son an admonition. “You have to be like invisible ink,” he said. “You will leave traces of your existence when, in...