The former First Lady’s new book, “Melania,” promises to draw back the drapery and expose the person behind the persona. It obscures more than it reveals.

Depending on how you define “memoir” — must it be a coherent narrative, or does a posthumous collection of diary entries suffice? — roughly a dozen first ladies of the United States have penned a total of more than 20 accounts of White House life ( Hillary Clinton, who simply will not be stopped, is responsible for four on her own).