Jensen Huang, the C.E.O. of Nvidia and one of the most important leaders in A.I., has admitted to having an affair with a woman believed by U.S. intelligence to be a Chinese spy. (China denies the allegations.) I caught up with Stephen Witt, who has written extensively about Huang—including in The New Yorker and in “The Thinking Machine,” his book about Nvidia—to discuss the fallout from the news. The following conversation has been edited and condensed. Why does this matter?