Greta Thunberg is “mentally ill.” Emma González is a “skinhead lesbian.” David Hogg is “a special kind of stupid.”

These may sound like playground taunts, but they’re not: All are epithets applied by politicians, pundits or political elites (adults) to the young leaders of global movements against climate change and gun violence. Fox News guest Michael Knowles offered the first observation; the second came from Leslie Gibson, a former Republican candidate for the Maine State House (who dropped out because of the remark); Virginia Thomas, the wife of Supreme Court Justice Clarence Thomas, delivered the third.

Thunberg is 16, and González and Hogg are in their late teens.

This kind of rhetoric, experts say, is the hallmark of a new era of American political discourse: one that allows — even encourages — vitriolic verbal abuse of children and teenagers.

“There used to be a constraint upon criticizing children, generally,” said Lawrence Prelli, a University of New Hampshire professor who studies political discourse. “These vile attacks now are a sign of the times ... when I look back into the past, it’s really hard to find examples beyond this recent period.”

Justin B. Richland, a University of California at Irvine professor and anthropologist who studies language, said he finds the trend troubling.

“I’m paying attention to it; I’ve been thinking a lot about it,” Richland said. “This particular moment has just become so piqued for this.”

He and other analysts had a variety of theories for how the country arrived at a place where it’s par for the course for Fox News host Laura Ingraham to suggest Thunberg and other youth climate activists are “brainwashed,” evil and demented — or for President Trump to mock the 16-year-old to his almost 65 million followers on Twitter.

But young liberal activists are not the only targets of this type of heated rhetoric — conservative figures have drawn fire, too. Notably, a former Republican representative compared pro-gun rights Parkland shooting survivor Kyle Kashuv to a school shooter; and 16-year-old Nick Sandmann earned denunciations from a wide range of prominent figures after a widely publicized encounter with a Native American activist at the Lincoln Memorial.

In part, it’s because young people are more prominent and politically active today than at any other moment in recent history, Prelli said. The fact that the campaigns against both climate change and gun violence are being led “front and center” by teenagers — and involve scores of young people as rank-and-file members — is “unusual,” to say the least, according to Prelli.

Rose McDermott, a Brown University professor who studies political psychology, traced the phenomenon to Malala Yousafzai and her 2014 acceptance of the Nobel Peace Prize. Yousafzai, who was 17 at the time, earned the prestigious award for her efforts to ensure all people, but especially women and children in her native northwest Pakistan, have the right to an education.

“Her getting that award at such a young age changed the political gravitas around younger people being able to be powerful forces for change, and spokespeople for issues of change,” McDermott said.

Youth advocates’ rise to prominence was also fueled by advances in technology and social media, according to McDermott. Over the past decade, sites including Facebook, Twitter and Instagram — coupled with the rise of smartphones — have displaced traditional media distribution platforms such as newspapers and cable TV, she said.

That means young people can deliver immediate, unfiltered messages that earn them huge followings and influence unthinkable in a pre-iPhone era, McDermott said. Hogg, González and others wielded their Twitter accounts to gain international attention as they fought to end gun violence in the wake of a deadly shooting at their Parkland, Fla., high school in February 2018. Thunberg’s path to fame began when she posted an Instagram picture of herself sitting outside Sweden’s parliament building to protest government inaction on climate change in August 2018.

But as youth advocates emerged into the spotlight, they also became targets for criticism. To some extent, that’s fair, Prelli said.

For example, “because Greta is at the foreground of this movement, she is a legitimate target for criticism about what she’s advocating,” Prelli said. “But when you start attacking her in this way that denies she’s a normal human being … that just seems out of bounds.”

The increasing nastiness of attacks launched against young activists reflects a broader shift in American political discourse, experts said. The tone of discussion — whether between adults or directed at children — has become vastly more juvenile and insulting in recent years, said Thomas Gustafson, a professor of English and American studies at the University of Southern California.

“We have witnessed many forms of decorum broken in our politics, with President Trump taking a lead in bringing tabloid sensationalism and below-the-belt verbal punches,” Gustafson said. “The ad hominem attacks on Hogg and Thunberg are another blow.”

Others also pointed to Trump as a catalyst, blaming both his language and his policies. The president is well known for name-calling and for issuing highly personal attacks on opponents.

Trump views these kinds of comments as proof he is more genuine than other politicians — he wants to be seen as “telling it like it is,” Prelli said. Public figures across the political spectrum have followed suit, creating a world where “you can start saying vile things that people in the past would not put forward,” Prelli said.

McDermott, meanwhile, pointed to the Trump administration’s policy of separating immigrant children from their parents at the U.S.-Mexico border.

“When you have a society accepting the wide-scale separation of kids from parents, that allows the maltreatment of kids at the border, it’s not that far a leap to start treating political opponents — even if they’re kids — more badly,” she said.

It’s too soon to say whether this new age of nasty rhetoric will permanently reshape American politics, experts said.

Besides, though we may be living through a new low, the country has a long history of political name-calling, Gustafson said.

He noted that Washington Irving, an essayist, historian and diplomat of the 19th century most famous for writing the short story “Rip Van Winkle,” once dubbed the U.S. government a “logocracy” in which politicians and newspapers fought battles of words and engaged in “slangwhanging.”

Irving “would not be surprised at all by Twitter insults,” Gustafson said. “But I suspect he would be appalled at ad hominem attacks on figures too young to vote.”