Copyright The New York Times

Michelle Obama’s new book, “The Look,” is a lot of things. It is an Amazon best seller. It is a glossy photo book full of fashion. It is the story of the expectations that were heaped upon the first Black first lady. And it is the third installment of a trilogy of books by Mrs. Obama that focus on self-realization, including her memoir, her advice book on overcoming adversity and, this time, a meditation on the power of clothes. But most of all it is a historical document, capturing a pivotal moment in the evolution of the role of first lady when clothing became a key part of communication. When, in other words, dress became an officially recognized part of the job. That’s a bigger deal than it might appear.