Curtis Sittenfeld likes to imagine the sex lives of presidents.(snip) She does it again in “Rodham,” her new novel, to be published on May 19. I won’t soon forget the scene in which Bill Clinton and Hillary Rodham distract themselves while driving through Arkansas in a way that redefines “joy ride.” “Please don’t get pulled over,” Hillary cautions him. Did this happen? Who knows? The fascination of the first third of “Rodham” is its weave of history and hypothesis as it chronicles the initial meeting of Bill and Hillary at Yale Law School, their courtship and her migration to Arkansas...