The morning after Hillary Clinton eviscerated Donald J. Trump for his demeaning comments about women, Mr. Trump called into Fox and Friends and doubled down.

“I know that person,” he said. “That person was a Miss Universe person. And she was the worst we ever had, the worst, the absolute worst, she was impossible. She gained a massive amount of weight.”

The person in question is Alicia Machado, the Miss Universe winner in 1996. Mr. Trump threatened to fire her and then invited reporters to watch him put her through a workout. He called her “Miss Piggy,” as Mrs. Clinton reminded the audience last night.

“That joke caused me a lot of pain,” Ms. Machado said in a video the Clinton campaign posted soon after the debate.

Mr. Trump has long had a fixation with women’s weight, and many have felt the sting of his mockery. Join the club. Like most women I know, I’m obsessed with weight and bombarded with cultural messages reinforcing that obsession. Skinny jeans. Clingy knits. Flat bellies. Tight torsos. Low-carb diets. French-women-don’t-get-fat diets. The voices on the outside are often echoing the ones on the inside.

What Mr. Trump doesn’t seem to understand is that when men talk about what women look like, what women hear is somebody saying, “There’s something wrong with you.” Sadly, women are still too vulnerable to that message.

The question of appearances has bedeviled this campaign — a contest between a 70-year-old man who likes to surround himself with women he considers beautiful and a 68-year-old woman whose changing hairstyles and clothing choices have been mercilessly chronicled.

Sexism watchers have been ready to pounce on any comments about Mrs. Clinton’s sartorial choices; they’ve largely been disappointed. But last night, Mr. Trump veered into dangerous territory when he seemed to repeat a criticism that Mrs. Clinton lacked a presidential “look.” Then his lob at her stamina backfired, allowing her to hit back with one of her most caustic and, analysts said, most effective retorts. “As soon as he travels to 112 countries,” she said, and matches her list of diplomatic achievements, “he can talk to me about stamina.”

The Twittersphere lit up with jabs at Mr. Trump’s sniffles. Two, it seemed, could play at the appearance game.

Susan Chira is a senior correspondent and editor on gender issues for The New York Times.