From repealing climate policies to overturning guidance on the safe development of artificial intelligence (AI), Republican Donald Trump made plenty of promises during his presidential campaign that could affect scientists and science policy. But fulfilling all of his pledges won’t be easy.

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Trump, now the US president-elect for a second time, will have some advantages as he re-enters the White House in January. The first time he took office, in 2017, his victory was a surprise, and many government watchers who spoke to Nature say he didn’t have a solid plan. By contrast, the Trump administration that enters office next year will be better prepared, and Trump himself is likely to face fewer checks on his power now that he has consolidated control over the Republican establishment, says Matt Dallek, a political historian at George Washington University in Washington DC who studies the evolution of the modern conservative movement.

But that doesn’t mean he will be able to do as he pleases, Dallek adds. “There’s a kind of revolutionary sweep to a lot of Trump’s promises that may collide with the messy reality of implementation.”

Here Nature talks to policy and other specialists about what might be in store on a range of science issues during a second Trump administration.

Artificial intelligence

Trump, who is industry-friendly, has promised to repeal US President Joe Biden’s executive order on AI, a guideline released last year for developing the technology safely and responsibly. Trump’s pledge echoes the Republican party’s platform, which says that the executive order “hinders AI Innovation”.

Given that executive orders can be revoked by a president at any time, it will be possible for Trump to implement his plan as soon as he enters the White House. But what will he put in its place?

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“The emphasis will shift away from the regulatory environment” and towards technology companies making their own voluntary decisions on safety, says Suresh Venkatasubramanian, director of the Center for Technological Responsibility, Reimagination, and Redesign at Brown University in Providence, Rhode Island. Venkatasubramanian says he is “sceptical that that will be enough” to address AI-associated risks to public safety, data-privacy concerns and the use of biased algorithms that disadvantage certain groups of people.

Biden’s executive order emphasized the need to ensure that AI models, which are trained on human-derived data, don’t output discriminatory results. That’s probably also not going to be a heavy priority for the new administration, Venkatasubramanian says. The Republican platform says that it will “support AI Development rooted in Free Speech and Human Flourishing”.

According to Roman Yampolskiy, a computer scientist and AI safety researcher at the University of Louisville in Kentucky, “it is a great idea to remove censorship and support free speech” in general. But, he says, “removing regulations around training of advanced AI systems is the worst possible thing we can do for the safety of the American people and the world”. Given the risks associated with developing superintelligent AI systems, which could potentially operate in unpredictable ways and cause harm to humans, Yampolskiy and other AI researchers have been arguing for a pause in AI development, which could only be achieved with stronger regulation.

Climate change

Many federal climate efforts are likely to stall or move in reverse under Trump, who has long denied the dangers of climate change while prioritizing the economic benefits of boosting domestic fossil-fuel production. Even so, policy specialists say that Trump is unlikely to stop the United States’s gradual shift towards clean energy.

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For instance, it will not be easy to undo Biden’s signature climate achievement: the 2022 Inflation Reduction Act (IRA), which created a raft of federal investments, now estimated at more than US$1 trillion, in climate and clean energy that are scheduled to run until around 2032. Repealing that legislation would require an act of the US Congress. But even if Republicans end up in control of both congressional chambers, businesses and leaders in conservative US states that are already benefiting from IRA investments might not be eager to cut off the flow of federal money, says Joanna Lewis, who heads the Science, Technology and International Affairs Program at Georgetown University in Washington DC.

Trump could have a bigger — and more negative — impact on climate progress if he moves to weaken climate regulations put in place for things such as power plants and automobiles. Similarly, his promise to put new tariffs on goods from countries such as China and Mexico could actually increase the cost of clean-energy technologies, says David Victor, a political scientist at the University of California, San Diego.

The president-elect has also promised to once again pull the United States out of the 2015 Paris agreement, which commits member countries to limiting global warming to 1.5–2 °C above pre-industrial levels. Trump’s administration had to wait until 2020 before formally leaving the agreement last time, and Biden moved to rejoin the agreement soon after taking office several months later. But under the rules of the agreement, the leaving process would take only one year this time around.

Many climate observers say the absence of the United States — the world’s second-largest greenhouse-gas emitter — from the pact could reduce pressure on China and other nations to scale up their efforts to curb emissions just as time is running short. “This is a pivotal decade for climate action, and four more years of Trump could be disastrous in terms of mobilizing climate action,” Lewis says.

Health

In the weeks leading up to the US election, Trump teamed up with political figure Robert F. Kennedy Jr on a platform promising to “make America healthy again” by tackling the root causes of chronic diseases, removing toxic substances from the environment and combating corporate corruption. Trump has said that he will let Kennedy, who has questioned vaccine safety, “go wild on” health, unnerving public-health and health-policy researchers.

It remains to be seen whether Trump will appoint Kennedy to a position such as director of US Health and Human Services (HHS) — or whether the US Senate would approve such a move — but it’s clear that Kennedy will have Trump’s ear on health issues.

Georges Benjamin, the executive director of the American Public Health Association in Washington DC, worries about Kennedy’s role in the new administration because he has long cast doubt on the vaccine-approval process, threatening to undermine confidence in the jabs and cause a resurgence in illnesses such as measles. “People will get sick and die because of the confusion around vaccines, if [Kennedy and Trump] implement some of the things they verbalize,” he says.

Some of Kennedy’s goals, such as cracking down on ties to industry at regulatory agencies such as the US Food and Drug Administration, are good, says Diana Zuckerman, president of the National Center for Health Research, a non-profit think tank in Washington DC. But those goals don’t jibe with what occurred during the first Trump administration, when Trump installed people in important health posts who had close industry ties, such as former HHS director Alex Azar, so it’s hard to know what will happen, she says.

Considering Trump’s isolationalist approach and his past comments criticizing the World Health Organization, support for global health is also likely to be “greatly scaled back” during Trump’s second term, says Ezekiel Emanuel, a bioethicist and long-time observer of the US biomedical funding landscape at the University of Pennsylvania in Philadelphia. The United States is “the key player” in the funding of global-health initiatives, says Emanuel. This includes, for instance, a programme that aims to end the global AIDS epidemic. So it’s “hard to be optimistic” about the future, he adds.

Foreign science partnerships

During Trump’s first term, his administration barred people from half a dozen countries that it said were “compromised by terrorism” from entering the United States and implemented an anti-espionage programme called the China Initiative that led to the arrests of a number of scientists of Chinese heritage. Although the Biden administration overturned the travel ban and ended the China Initiative, federal officials have continued efforts to guard against foreign interference in US research.

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Specialists says it’s unclear whether the second Trump administration will revive the China Initiative, although the Republican-led US House of Representatives advanced legislation in September that would do so. But a reinstatement of the travel ban is likely, says Adam Cohen, a lawyer at Siskind Susser in Memphis, Tennessee, who focuses on academic immigration and who says the president has broad authority to institute such policies.

Like the first Trump administration, the new one will probably clamp down on granting visas to foreign researchers and students from some countries, says Jennifer Steele, an education-policy researcher at American University in Washington DC. Policies that make it harder for international and US researchers to meet would also make it harder for new scientific collaborations to arise, says Caroline Wagner, a specialist in science, technology and international affairs at the Ohio State University in Columbus. That’s because such partnerships are fuelled by face-to-face contact. “Collaborations don’t begin with people just e-mailing each other across the miles,” she says.

But there might be one bright spot on the collaboration front, at least for US–China partnerships. Denis Simon, a non-resident fellow at the Quincy Institute for Responsible Statecraft, a foreign-policy think tank in Washington DC, thinks that a crucial pact governing US–China scientific cooperation that has been expired for the past year is likely to be signed by the Biden administration before Trump’s second inauguration in January. Although a renewed agreement would probably be more limited in scope owing to increased US–China tensions, its existence would show that “both governments give their blessing” to collaborations, Simon says.