On a conference call to prepare for a recent debate, Barack Obama brainstormed with his top advisers on the fine points of his positions. Michelle Obama had dialed in to listen, but finally couldn't stay silent any longer.

"Barack," she interjected, "Feel -- don't think!" Telling her husband his "over-thinking" during past debates had tripped him up with rival Hillary Clinton, she said: "Don't get caught in the weeds. Be visceral. Use your heart -- and your head."

The...