In March 2017, an engineer at G.E. Aviation in Cincinnati received a request on LinkedIn. The engineer, Hua, is in his 40s, tall and athletic, with a boyish face that makes him look a decade younger. He moved to the United States from China in 2003 for graduate studies in structural engineering. The LinkedIn request came from Chen Feng, a school official at the Nanjing University of Aeronautics and Astronautics, in eastern China. Days later, Chen sent him an email inviting him to the university to give a research presentation. Hua arranged to arrive in May, so he could attend a nephew’s wedding and his college reunion at Harbin Institute of Technology. There was one problem, though: Hua knew that G.E. would deny permission to give the talk if he asked, which he was supposed to do. He went to Nanjing, and flew back to the United States after the presentation. He thought that would be the end of the matter. Many scientists and engineers of Chinese origin in the United States are in...