On Thursday, Donald Trump tweeted that MSNBC’s Mika Brzezinski had been “bleeding badly from a face-lift” when she visited Mar-a-Lago last December. On Tuesday, in the Oval Office, he interrupted a phone call with the Irish prime minister to call over a female Irish journalist, Caitriona Perry, while referring to her “nice smile” and “this beautiful Irish press.”

The incidents are two sides of the same coin. Two decades ago, a pair of social psychologists, Susan Fiske and Peter Glick, distinguished between what they called “hostile” and “benevolent” sexism. Hostile sexism manifests itself in derogatory or threatening comments about a woman’s appearance, capacities, or behavior. Benevolent sexism, by contrast, manifests itself in praise or chivalry that nonetheless reaffirms a woman’s subordinate status. Telling your female coworker that she’s ugly is an expression of hostile sexism. Telling your female coworker that she’s pretty is an expression of benevolent sexism. Sexually assaulting a female colleague is an expression of hostile sexism. Suggesting that a female colleague needs help carrying her bags is an expression of benevolent sexism. Hostile sexism may be more antagonistic and aggressive but benevolent sexism also conveys the message that women should be valued for their appearance, and that they are not equal to men.

The more a woman conforms to traditional gender norms, the more likely she is to experience benevolent sexism. The more she threatens them, the more likely she is to experience hostile sexism. Take sexual harassment, a particularly violent form of hostile sexism. According to the University of British Columbia’s Jennifer Berdahl, the best predictor of whether a woman will be sexually harassed is whether she is considered “uppity.” The women most vulnerable to sexual harassment are those “with relatively masculine personalities (e.g., assertive, dominant, and independent)” and those who perform jobs traditionally done by men.

Hostile and benevolent sexism, in other words, are different expressions of male power. As Julia C. Becker and Stephen Wright explain, they are “complementary tools of control, the stick and the carrot, that motivate women to accept a sexist system.”

Trump’s behavior towards Brzezinski and Perry fits this theory perfectly. He insulted Brzezinski’s appearance (hostile sexism) but praised Perry’s (benevolent sexism). Why? Because Brzezinski posed a threat. His attack came moments after she had finished lampooning his fake Time cover on the air. Perry, by contrast, had not challenged Trump. She had been standing in his office while he conducted a feel-good conversation with the Irish prime minister. To use Berdahl’s language, she had done nothing that Trump might construe as “assertive, dominant,” or “independent.”

One can see a similar pattern in Trump’s previous sexist comments: When women challenge him politically, he often insults them physically. In August 2015, after Megyn Kelly asked him a tough question at a GOP debate, Trump said “You could see there was blood coming out of her eyes, blood coming out of her wherever” and later called her a “bimbo.” In September 2015, while Carly Fiorina was rising in the polls, he exclaimed, “Look at that face! Can you imagine that, the face of our next president?’” In July 2016, while Elizabeth Warren was savaging him on the campaign trail, he told a rally: “You find anything nice about her cheekbones? I dunno. So, look at her cheekbones.” After his second debate with Hillary Clinton, he said she had “walked in front of me. Believe me, I wasn't impressed.” That same month, when journalist Natasha Stoynoff accused Trump of having harassed her in 2005, he responded, "Take a look, you take a look, look at her, look at her words—you tell me what you think. I don't think so."

By contrast, when Trump finds women non-threatening, he often responds with benevolent sexism. He delighted in walking through the beauty pageants he owned—where the young contestants were entirely beholden to him—commenting on how gorgeous they were. He even repeatedly praised the beauty of his own daughter.

Viscerally, Trump likely understands what the research shows: that focusing people’s attention on a woman’s appearance makes them value her abilities less. For a 2009 study in the Journal of Experimental Social Psychology, Nathan Heflick and Jamie Goldenberg asked one group of college students to write about Sarah Palin’s appearance and another to write about her “human essence.” Then both groups were asked a series of questions about her. The students who had written about her appearance rated her as less competent. In a different study, participants told to focus on Michelle Obama’s looks deemed her less competent, too.

What Trump may not grasp is the different effects benevolent and hostile sexism have on the women who experience them. Jennifer Bosson, a professor of psychology at the University of South Florida, told me that, “benevolent sexism reminds women of male protection and of the benefits of being pretty. It can leave women immobilized.” Hostile sexism, by contrast, “pisses women off. They get motivated to fight back.” As Becker and Wright put it, “benevolent sexism undermines, whereas hostile sexism promotes social change.”

Hostile sexism seems to motivate women even when they merely observe it happening to others. A 2010 study by Stephenie Chaudoir and Diane Quinn of the University of Connecticut found that merely hearing a man speak in demeaning sexual terms to another woman made female college students “feel greater anger and motivation to take direct action toward men.”

There’s some evidence that Trump’s hostile sexism, as evidenced most infamously in the Access Hollywood tape released last October, has had exactly that result. A post-election study found that people who were more angered by Trump’s comments about women were more likely to take political action to oppose him. This January’s women’s march in Washington was the largest in American history.

That’s the good news. The bad news is that while women often initially react to hostile sexism with outrage and a desire to reassert their dignity, the effects of persistent hostile sexism can be debilitating. A 1993 study by the University of Illinois’s Louise Fitzgerald found that women who suffer ongoing sexual harassment or disparagement “experience lower morale and job satisfaction and increased absenteeism, anger, anxiety, depression, and physical illness symptoms.”

Could something similar happen to American women writ large? Could they too move from indignation to demoralization as Trump again and again sexualizes and demeans his female critics? It’s an experiment Trump seems determined to conduct.