Tens of thousands of people around the world rallied for rational thought on Saturday, and those who attended the main March for Science, in Washington, D.C., were treated to a lengthy program of distinguished speakers: astronauts, astronomers, neuroscientists, biologists, chemists, and other Americans who—in a truly rational society—would be famous. But only one of them was legitimately famous.

“Our numbers here today show the world that science is for all,” Bill Nye the Science Guy belted to the crowd on the National Mall. “Our lawmakers must know that science serves every one of us. Every citizen of every nation in society. Science must shape policy. Science is universal. Science brings out the best in us. With an informed, optimistic view of the future, together we can—dare I say it—save the world!”

This speech, the Washington Post declared, “was a significant moment—for science, for William Sanford Nye and for the masses who have followed him for decades, from fuzzy TV screens in their middle school classrooms to the grounds of the Washington Monument at Saturday’s March for Science.” But Nye’s inspiring words were also, perhaps, a plug for his new Netflix show: Bill Nye Saves the World.

At least he had the good sense on Saturday to say “we” can save the world, not “I.”

The Science Guy is everywhere these days. He’s on Reddit, answering questions about whether he’ll run for president. He’s winning awards for his social media prowess. And he’s a talking head on your cable news channel of choice. Such ubiquity has become self-perpetuating, as he’s now become, to some observers in mainstream media, the national spokesman for science in an age of “alternative” facts. “He has become more than the zany educator-entertainer who charmed kids with cartoonish sound effects,” the Post glowed. “He is an activist for science, leading those now-grownups into political battle.”

Nye’s rise, as some see it, couldn’t have come at a more critical time. President Donald Trump has repeatedly called global warming a “hoax,” and is threatening massive budget cuts that will gut government funding of science and put many scientists out of work. But it’s worth asking: Is Nye really the right guy for the job? He’s not even a practicing scientist; though he has a bachelor’s degree in mechanical engineering, he hasn’t worked as an engineer for more than 30 years. Considering the entire span of the 61-year-old’s career, it’s much more accurate to call him an entertainer. After all, he’s called “Bill Nye the Science Guy” because of his eponymous PBS show in the ’90s.

Nye’s response to this critique, as he said to the Post, is that “it doesn’t take ... a meteorologist to comprehend the perils of climate change.” That is true. But comprehending climate change is one thing; explaining it and defending it effectively is another. Historically, Nye has done that; lately, not so much. It seems that years of political debate have made him too jaded, exasperated, strident, and partisan to be the face of the climate change fight. Worse, he’s unwittingly feeding the conservative narrative that the left’s reverence for science is all just a political performance.

Marsha Blackburn helped Bill Nye become the famous science activist he is today. In February 2014, the Republican congresswoman from Tennessee appeared with Nye on NBC’s Meet the Press, where she claimed that carbon dioxide is not harmful and that the amount of carbon in the atmosphere—400 parts per million at the time—“is very slight.” Nye rebutted her with a science lesson, stating that the real problem was the rate at which carbon was being added to the atmosphere: In 1965, there was 320 parts per million. “My god, that’s a 30 percent increase,” he said. (It’s actually 25 percent, but you get the idea.)

“Nye did everything you’re supposed to during a televised exchange of talking points: He spoke in digestible, declarative sentences, returning over and over to concrete examples for his arguments,” Emmett Rensin wrote the New Republic at the time. “More important, he kept his cool ... while Blackburn mumbled semi-coherently.” Nye didn’t convince Blackburn that climate change was real, but anyone on the fence would have fallen to his side.

Rensin’s wondered whether “this genial, bow-tied eccentric really the most qualified and effective person for the job,” but ultimately answered in the affirmative. And rightly so. But since then, Nye has increasingly lost his cool. He’s also lost his skill at effectively explaining and defending the scientific evidence of climate change.

In a recent debate on CNN, William Happer, the Princeton physicist Trump reportedly is considering to be his top science adviser, argued not only that excessive carbon dioxide isn’t harmful, but that it’s actually good for the planet. “There’s this myth that’s developed around carbon dioxide that it’s a pollutant, but you and I both exhale carbon dioxide with every breath. Each of us emits about two pounds of carbon dioxide a day, so are we polluting the planet?” Happer said. “Carbon dioxide is a perfectly natural gas, it’s just like water vapor. It’s something that plants love, they grow better with more carbon dioxide, and you can see the greening of the earth already from the additional carbon dioxide in the atmosphere.”

Nye’s response should have been easy. Yes, we all exhale carbon dioxide—around 3 billions tons per year—but human breathing is a net zero in terms of carbon dioxide emissions. Plants absorb carbon dioxide from the atmosphere, so when we eat plants—or eat animals that eat plants, or eat animals that eat animals that eat plants—we ingest that carbon. When we exhale, we’re simply returning that same amount of carbon to atmosphere. There is no such “closed loop” for the some 35 billion tons of carbon dioxide that fossil fuel combustion adds to the atmosphere every year, which is why the planet is warming.

But Nye didn’t say any of this. Instead, he pivoted, and scolded CNN for allowing a climate-change denier to speak with the same authority as mainstream climate scientist. Nye isn’t wrong, exactly, to criticize CNN for giving Happer a platform, but he also knows better than anyone that this is how cable news conducts climate change debates. The old Nye would have played along. He would have challenged Happer’s ignorance, and educated CNN viewers on the harms of greenhouse gases.

This was not an isolated case. A few weeks earlier, Nye was a guest on Tucker Carlson’s evening show on Fox News. It was a cringeworthy nine minutes of television.

“To what degree is climate change is caused by human activity?” Carlson asked.

A simple question, but one that gave Nye pause. “To a degree that it’s ... that it’s a very serious problem in the next few decades,” he said.

“But to what degree? Is it 100 percent? Is it 73.4 percent?”

“The word degree is a word that you chose, but the speed to which climate change is happening is caused by humans.”

“But to what extent is human activity is responsible for speeding that up? Please be more precise.”

Carlson said Nye looked annoyed—and he was right. Nye then tried to change the subject, asking Carlson why he doesn’t consider climate change a problem.

This whole exchange could have been avoided if Nye had simply said that humans have caused at least half of the observed warming since 1950, and most likely all of it, according to the Intergovernmental Panel on Climate Change.

Climate-change deniers like Carlson perpetuate scientific illiteracy by questioning every fact, under the guise of journalistic scrutiny. Nothing is certain, and everything is up for debate. “You don’t actually know because it’s unknowable,” Carlson said.

But it is knowable; the answers do exist. Bill Nye just didn’t have them.

The climate fight is, at its core, a fight for public opinion—and science is losing that fight. A Pew Research poll in October found that more than three quarters of Republican voters and nearly a third of Democratic voters don’t think climate change is caused primarily by human activity. Clearly, yelling at the public that “97 percent of scientists agree” that humans are causing climate change—a mantra that the left, most famously John Oliver, has been repeating for years now—isn’t working.

But the first episode of Bill Nye Saves the World is essentially just that, stretched out over 31 minutes. “Earth Is a Hot Mess” begins promisingly, with Nye using a beaker and a flame to demonstrate how adding heat to water makes it rise. But then it gets weird. Nye sends supermodel Karlie Kloss to explain to the rapper Desiigner how climate change will impact his beloved sushi and coffee. After that, Nye assumes the audience is on his side. “I expect the United States to be the world leader in addressing a problem like climate change,” he says. “But is the United States the world leader? No. Why? Because the deniers. The climate change deniers have been so successful.”

This is likely the point where viewers who aren’t already on Nye’s side—the ones who need to be convinced of climate change’s reality—would switch to The Walking Dead, if they hadn’t already. It’s less what Nye is saying than how he says it. “Nye’s skepticism verges into meanness,” Vox’s Aja Romano wrote. That meanness is alienating, even to those who might agree with him on the substance. “Nye and I are on the same team—and yet I still felt like I was being talked down to throughout his show,” Gizmodo ‘s Maddie Stone wrote. “How will the average viewer feel?”

We can guess how the average conservative viewer feels. Right-wing media has had a field day with Nye lately. After his debate with Happer, the Blaze cackled with delight: “Bill Nye blows gasket when a real scientist schools him on facts.” National Review called Nye’s performance with Carlson “embarrassing,” citing his inability to say the degree to which humans are responsible for climate change. Nye’s Netflix show proves he’s not an actual “science guy,” as another Blaze article posited, but a science lover in performance only. Ben Shapiro argued that Nye is like most progressives in this way:

This is the dirty little secret of the Left’s sudden embrace of Science™—it’s not science they support, but religion. They support that which they believe but cannot prove and do not care about proving. Bill Nye isn’t interested in a scientific debate about global warming—how much is occurring, the measurement techniques at issue, the sensitivity of the climate to carbon emissions, the range of factors that affect the climate. He wants you to accept his version of the truth—not just that global warming is happening, but that massive government intervention is necessary in order to avert imminent global catastrophe.

The idea that liberals worship science without regard for nuance isn’t restricted to the political right; it’s a debate within the scientific community itself. Writing in Slate this week, physician Jeremy Samuel Faust noted that many of the millennials who marched for science are the same people who share pseudo-scientific articles about how beer makes you smarter. “Being ‘pro-science,’” he wrote, “has become a bizarre cultural phenomenon in which liberals (and other members of the cultural elite) engage in public displays of self-reckoned intelligence as a kind of performance art, while demonstrating zero evidence to justify it.”

The problem is not Nye’s understanding of the science. It’s that he’s become unable to explain it, in simple and clear terms, to a skeptical audience. Maybe he’s been defending science for too long now, and has grown tired of debating conservative cranks whose very job is to reject everything he says. Or maybe he’s become enamored with his celebrity, and has discovered that—like the cable-news pundits and hosts he tussles with—being performative is a more lucrative path than honest inquiry and factual rigor. But so long as a partisan performance artist is the national face of the climate change fight, conservatives will continue to have a case that the left’s championing of science is all about politics.

Tucker Carlson and his ilk are wrong about the truth of climate change, but they’re right about Bill Nye. The left needs a more effective, less divisive spokesperson for its cause. It’s time for a real science guy—or gal. And thanks to last weekend’s march, we have a long list of qualified candidates to choose from.