US election debate: what Harris and Trump said about science

Science issues took a back seat to the economy, immigration and national security during the first — and perhaps only — debate between US presidential candidates Kamala Harris and Donald Trump, on 10 September. But vice-president Harris and former president Trump did make passing references to subjects such as climate change and scientific competitiveness.
Neither candidate revealed much about the specific policies that they plan to implement if they win the November election. But that, researchers say, was not necessarily the point.
“We rarely learn anything of substance in a debate, but we do form impressions of who the candidates are as people,” says Matt Carlson, a media researcher at the University of Minnesota in Minneapolis. “And this debate offered a particularly stark contrast between Trump’s angry gut reactions and Harris’s optimistic outlook.”
Here, Nature analyses what the candidates did and did not say about science, and what researchers think of their stances.
This was a big topic in the debate. Harris said she supports reinstating the protections of Roe v. Wade — the US Supreme Court ruling that previously ensured the right to an abortion until the point that a fetus can survive outside the womb, typically around 23 weeks of pregnancy. The ruling was overturned in 2022 by a majority-conservative panel of justices, three of whom Trump appointed during his presidency. Trump said the decision about whether to ban abortion should be left up to each US state, and did not directly address whether he would veto a national ban if it came to his desk.

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Harris also discussed how state bans are affecting health care, saying that people experiencing miscarriages are being denied crucial care in emergency rooms. This is true, says obstetrician and gynaecologist Daniel Grossman, director of Advancing New Standards in Reproductive Health, a research programme at the University of California, San Francisco. Earlier this week, his team released a report detailing, among other things, how people with pregnancy complications have been put at risk because of delayed access to abortion care.
Trump said that abortion should be allowed in cases of rape, incest or when the pregnant person’s life is at risk. Grossman notes that implementing those exceptions is very difficult. “Medicine is not black and white,” he says. “How threatened does the life of the pregnant person need to be before someone is eligible for legal abortion?” Physicians, worried about criminal prosecution, are struggling with how to make such decisions, he says.
When asked about the economy, the candidates argued over tariffs. Trump touted tariffs that his administration put on goods from China, which he claims brought money into the economy. Harris clapped back, saying that, during his presidency, Trump was “selling American chips to China to help them improve and modernize their military”. The United States should focus on domestic innovation, she said, and that means “investing in American-based technology so that we win the race on AI [artificial intelligence] and quantum computing”.

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Although it’s true that during the beginning of the Trump administration, US companies — such as Nvidia in Santa Clara, California — were selling advanced semiconductor chips and high-performance GPUs to China. But as Trump’s tenure progressed, these technology exports became increasingly restricted, says Denis Simon, a non-resident fellow at the Quincy Institute for Responsible Statecraft, a foreign policy think-tank in Washington DC. The administration of Harris and US President Joe Biden imposed further restrictions and passed the Chips and Science Act, which authorized more money for US research agencies to foster innovation and boosted domestic semiconductor manufacturing.
It was a missed opportunity that Harris didn’t speak on this topic, Simon says, although he still thinks she came out on top in the debate. Regarding relations with China, however, he would have liked the candidates to outline clear policies. “It is the second largest economy in the world,” Simon says. “What China does or doesn’t do is an important part of shaping the international landscape.”
The United States can’t cut itself off from China, says Caroline Wagner, a specialist in science, technology and international affairs at The Ohio State University in Columbus. “We’ve gained a lot by having China in the knowledge system. You can’t close the door without getting your fingers stuck in it.” The world also can’t make any meaningful progress on global-challenge issues, such as climate change and food security, if the United States does not have a collaborative relationship with China, Simon agrees.
The candidates were directly asked about climate change at the end of the debate. Harris acknowledged that it is real and that climate-related disasters are affecting people’s lives, then touted the Biden administration’s historic investments in clean energy and advanced manufacturing. “We know that we can actually deal with this issue,” she said. Throughout the debate, however, Harris found herself on the defensive regarding energy production, particularly regarding controversial hydraulic fracturing — or ‘fracking’ — technologies. Fracking has enabled companies to expand extraction of oil and gas in the country, but can pollute groundwater and increase seismic activity. Although she once said that she was against fracking, she repeatedly emphasized her support for it while saying that she backs using a diversity of energy sources.

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Trump didn’t answer the question and instead talked about imports from China, ending with personal attacks on Biden. Earlier in the debate, however, he emphasized the need to boost fossil-fuel production and warned that a Harris administration would push the United States to depend on ‘windmills’ and solar-energy farms, which he claims occupy too much land and “are not good for the environment”. (It’s true that renewable-energy facilities can have a significant environmental footprint1, but researchers have argued that the damage wrought by the production and burning of fossil fuels, which cause millions of premature deaths annually owing to air pollution and are altering the climate2, are much worse.)
Michael Mann, a climate scientist at the University of Pennsylvania in Philadelphia, says that there is room for growth in Harris’s approach to tackling climate change. In line with the Biden administration, she takes a ‘demand-side approach’ to reducing emissions by incentivizing renewable energy, which is “not enough”, he says. But she at least embraces the scientific consensus and acknowledges the “catastrophic impacts on human health”. A second term for Trump, who once called climate change a hoax, “would be game over for climate action as we know it”, he says.
The biggest factor in energy and climate issues discussed during the debate might be tariffs and “the veritable arms race between the two parties to show who will be tougher on China”, says David Victor, a political scientist at the University of California, San Diego. This could drive up the cost of technology imports to the United States and disrupt clean-energy supply chains, he adds.
In the end, however, neither the candidates nor the debate moderators spent much time on climate change. “If this debate is a barometer of what will determine the election, it’s not climate and energy,” Victor says.