Since then, however, she has been anything but a public defender, and, in fact, has been defiant in her silence.

First ladies are expected to accept their husband’s infidelities and cruelty and to remain their strongest champions, no matter what the circumstances (and Mrs. Trump’s are, undoubtedly, extreme). Lyndon Johnson could be downright mean to his wife, Lady Bird, upbraiding her in public and comparing her with women he found more beautiful. But when he was upset about negative press coverage ahead of the Democratic National Convention in 1964, it was his wife who cheered him on. In a fawning letter, Mrs. Johnson wrote: “Beloved — You are as brave a man as Harry Truman — or FDR — or Lincoln. You can go on to find some peace, some achievement amidst all the pain. You have been strong, patient, determined beyond any words of mine to express.” It is hard to imagine Mrs. Trump writing anything of the sort to her husband.

They are expected to be adoring. Nancy Reagan, Ronald Reagan’s biggest fan, wrote in her memoir, “My Turn”: “I’d like to come back as Ronald Reagan. If he worries, you’d never know it. If he’s anxious, he keeps it to himself. Depressed? He doesn’t know the meaning of the word. He’s really as relaxed and hopeful as he appears.”

Hillary Clinton was the first first lady to run for office, but as progressive and groundbreaking as she was, she nonetheless made the decision to stand by her husband after he admitted his affair with the White House intern Monica Lewinsky, regardless of her own hurt and humiliation. The day after President Clinton testified before a grand jury and came clean to the country, Mrs. Clinton marched across the South Lawn together with Bill, their daughter, Chelsea, standing between them, holding both of her parents’ hands, as they headed for Marine One to embark on their annual summer vacation on Martha’s Vineyard. It was the photo-op the president needed.

Maybe Mrs. Trump is more like Michelle Obama than people think. Though the mutual affection of the Obamas was obvious, Mrs. Obama was also the first first lady to challenge people to accept a woman who refused to play the role of the saccharine, adoring spouse. “I can’t do that,” she said in 2007 Vanity Fair interview. “That’s not me. I love my husband. I think he’s one of the most brilliant men I’ve ever met, and he knows that. But he’s not perfect, and I don’t want the world to want him to be perfect.”