Few patterns in American history have proved as durable as this one: while Presidents are attacked by their opponents for what they do or fail to do, First Ladies are disparaged for who they are. What's more, the unattractive traits that presidential spouses have been assigned don't seem to change. They're vain and frivolous (Jacqueline Kennedy in her designer gowns). They're pushy and calculating (Hillary Clinton and her health-care plan). They're irrational and superstitious (Nancy Reagan and her astrologer).
Or they're all of the above--and loony too. That was Mary Todd Lincoln's uniquely miserable lot: to be despised in nearly every...