A few years ago at a White House Correspondents' dinner, I met a very beautiful actress. Within moments, she blurted out: "I can't believe I'm 46 and not married. Men only want to marry their personal assistants or P.R. women." I'd been noticing a trend along these lines, as famous and powerful men took up with the young women whose job it was to tend to them and care for them in some way: their secretaries, assistants, nannies, caterers, flight attendants, researchers and fact-checkers. Women in staff support are the new sirens because, as a guy I know put it,...