In this months's US federal election, Donald Trump and his Republican party won the presidency, the senate and will likely win control of the House, bringing the Republicans under their mercurial leader into complete or near-complete control of the US federal government. Trump is obviously a polarizing figure, and there are many reasons for Americans to be concerned about his domestic policy agenda, but as in all US elections the choice of leader has global consequences. Here I will attempt to describe what I think will be the likely consequences for public and global health of a Trump presidency.
Obviously it's difficult to predict what a president will do, and harder with Trump than with most since his public statements are less controlled, more erratic, and often contradictory. He has made some big and bold claims, and at other times set himself at odds with his own party with some of his statements on, for example, IVF and abortion. At the same time, a powerful force of extremely reactionary people gathered around him have written a dangerous blueprint for how he should exercise power in the presidency, called Project 2025 - Trump himself disavows this document but it could reflect the general policy drive of his first period in office. We also cannot know clearly the political aims of the "techbros" like Peter Thiel, Marc Andreesen and Elon Musk, who have supported him and have strong but not always consistent or clear political opinions.
Despite these limitations, I think it is possible to give a broad overview of the direction of public and global health under his leadership. It's not pretty, and we should prepare ourselves for major changes in the global health landscape.

Domestic public health

Trump has stated that he wants to reduce government spending, and this is always a priority of Republican administrations, though they usually end up spending more in order to finance tax cuts. Trump has even discussed replacing income tax with tariffs, though it's difficult to say if he really means that or will be able to do it, and has joked (?) about putting Elon Musk in charge of cutting government "waste". This almost always means cuts in social security, health and welfare spending, which are just over 50% of the entire federal budget. Given reluctance to cut defence spending and the the sheer size of the welfare/health budget, it is likely that the USA will see cuts in medicaid expenditure, social security funds, and funding for public health. Trump himself has denied any plans to interfere with the Affordable Care Act ("Obamacare") or social security, but the Republican movement are obsessed with destroying Obamacare and, with a majority of two seats in the Senate, may actually be able to do what they famously failed to do in in his first term. Social security "reform" has also been a Republican dream since the 1990s, and although Trump has promised not to touch it, it's unclear whether he really cares. So we should expect sizable cuts to health and welfare spending, especially in medicare and medicaid and programs related to Obamacare. There will also likely be huge pressure on less publicly acceptable health initiatives - for example, HIV prevention programs and school safe sex campaigns - as well as on basic preventive activities. We can expect that domestically, public health and health financing - the ability of ordinary people to access health care - will worsen significantly.

Women's health

Domestically women's health is going to be significantly affected by Republican government, with a broad-based attack on access to abortion, contraception and other aspects of maternal and child health. Trump has indicated he does not support a federal abortion ban and will leave the policy to the states, but this will still lead to radical changes in access to abortion across much of the US. The consequences of this are far-reaching, up to and including restrictions on access to out of state medical care and will likely affect poor and Black women more. With almost no chance of legal redress given the state of US courts, American women can expect to suffer significant attacks on their bodily autonomy.

This will affect women globally, too. Republicans will likely reintroduce or strengthen restrictions on funding for women's health overseas, ensuring that no money goes to programs that provide sex education or abortion care, and potentially also restricting contraception and family planning programs. This will be even more likely if large cuts are made to foreign aid, since Republicans will probably push to target these cuts most forcefully on areas of health that they do not like.

Development aid for health

The USA is a major funder of international programs for health care, through USAID, PEPFAR and binational agreements. Republicans have been rumbling about cutting these programs massively, and if Trump's government does choose to target this area they will likely drive huge cutbacks in funding for basic health programs. USAID affects almost every aspect of development aid for health, as well as major research programs like the Demographic and Health Surveys. It is also likely that cuts will be ideological, aimed at countries that have offended Trump or his backers, and at programs that target aspects of public health that the Republicans ideologically oppose. PEPFAR in particular is vulnerable here - this is a major program funding HIV prevention and treatment in low- and middle-income countries which has been one of the USA's biggest and best contributions to global health, but it is highly vulnerable ideologically and is already in Republicans' sights.

We can expect that this will lead to large shortfalls in funding for existing health programs and funding uncertainty that will lead to cancelation of planned programs, with consequences particularly for HIV prevention, maternal and child health programs, programs targeting malaria and parasites, and infectious disease control.

Health of marginalized people

Domestically the Republicans have a deep animosity towards anyone they consider to be non-conforming, such as LGBT people, sex workers, injecting drug users, irregular migrants and prisoners. We can expect an intense attack on LGBT people, in particular transgender people - there is, effectively, an open intention among conservative political movements in the English speaking world to eradicate transgender people from society, or at best to force them to live miserable lives in the gender they were assigned at birth. Anti-LGBT politics is often violent and intensely discriminatory, but we can also expect to see this ideology reflected in cuts to funding for organizations promoting sex education, sexual health and HIV testing, and legal restrictions on their ability to communicate ideas publicly. It is likely that access to hormonal treatment will be restricted, with knock-on effects for post-menopausal women. Previous governments in the USA have attacked sex workers, in particular through the SESTA and FOSTA laws, and it is likely that their will be no relenting on the politics of sex work in the USA. State governments have been trying to enact bans on pornography, which will affect both the lives of sex workers and, more broadly, the ability of ordinary people to access basic sexual health information on the internet. We can expect these attempts to be more effective and better coordinated once the Republicans have federal power.
Globally, this crackdown will likely lead to severe cuts in funding for organizations that might have any connection with sex worker health, migrant health or the health of other minorities. Funding for basic HIV and overdose prevention activities among injecting drug users will be cut, and it is also possible that the US will redouble its efforts to push prohibition and punishment approaches to drug use. Globally these cuts can be expected to undermine efforts to prevent the spread of HIV and viral hepatitis, and also lead to a growth in human trafficking and organized crime, which always flourish in prohibition environments.
This will happen domestically as well - the USA has a huge and growing opioid overdose epidemic, and is already struggling to implement the well understood harm reduction policies that can end this epidemic. We can expect America's overdose epidemic to remain unmanaged, and also to see further reductions in the wellbeing of the USA's already terribly-treated prison population, the largest population in the world living in some of the harshest conditions.

Vaccines

There are rumours that Trump is going to appoint Robert F Kennedy, a known vaccine skeptic, to manage this aspect of America's public health policies or even to be [director of Health and Human Services] (https://www.cbsnews.com/news/robert-f-kennedy-trump-short-list-hhs-secretary-allies-say/). If he is given real power this would be a disaster, as he would effectively ban vaccination or severely limit is effectiveness. This would obviously be a disaster for American women, who would become the only population in the high-income world still at risk of cervical cancer, but it would also be terrible for children if the MMR vaccine is restricted. It's worth noting that a vaccine does not have to be banned for the government to severely affect its coverage - we saw this in Japan when the government still financially subsidized the HPV vaccine, but stopped promoting it, leading to a rapid drop in coverage. America is already experiencing a crisis of communicable diseases in children, and a large, widescale weakening of MMR vaccination programs would lead to incredible waves of measles infection.
This would have global impact too, with the US becoming the world's largest exporter of measles cases, which would rapidly create outbreaks in other nations that do not have sufficient vaccination coverage. The impact would be magnified if development funding was made contingent on it not supporting vaccination, since many countries fund their vaccination programs through donor support.

International health architecture

The Republican party is openly critical of the WHO and has been demanding the US leave the WHO for years. The USA could do this under Trump, or cut or restrict funding, and might also leave other international agreements such as the International Health Regulations or various bilateral agreements on data sharing and policy. It is likely that collaborations between academics in the USA and countries that Trump doesn't like - such as China - will be restricted or broken, and many initiatives on infectious disease control and data sharing will be damaged. If Trump introduces migration bans or mass deportations, he will also severely damage relations with other countries, which will inevitably ultimately affect their willingness to cooperate with US government activities in health.

Planetary Health

The Republicans refuse to believe that global warming is real, or at least pretend not to believe it, and their entire energy and environmental policy framework assumes it is not real. Obviously with Trump in government there will be no action on climate change, which essentially derails global efforts to tackle the problem, since the US is a huge carbon emitter. But the Trump government's impact on planetary health is unlikely to end there. Republicans want to dismantle the administrative state by defunding or severely restricting the activities of organizations like the FDA (which regulates drug approvals), the EPA (which manages environmental risk) and the USDA (which manages farms and food hygiene). The US is already struggling with a huge bird flu outbreak that is being poorly monitored and managed, and if the Trump agenda is successful the gutting of these organizations will significantly increase the risk of outbreaks of disease from animals to humans. These institutions are also essential in policy changes to prevent the growth of anti-microbial resistance (AMR) in bacteria, a huge threat to health. Much of the growth of AMR is due to overuse of certain antibiotics in farming, and weakening the USDA will worsen this already serious problem. Naturally these problems do not respect borders, and cuts in these agencies domestically will ultimately have global impact.

War and genocide

Donald Trump has never seemed especially interested in war, but his Republican backers love it. It is possible that after he enters office he will end support for Ukraine in its war with Russia, which will lead to a rapid end to that war. I think this will be good for Ukrainian men, because the outcome of that war is already decided and the only question is how long it will take and how many will die. Ending it quickly - even on terms completely unfavourable to Ukraine - will prevent the destruction of an entire generation of young men. However, it is unclear whether Trump really cares about this issue either way, and it is possible he will leave decisions about funding and continuing wars to his national security advisors. If he does not control the House he may also use funding for the Ukraine war as a lever to control other budgetary aspirations, which will ensure Ukraine has enough money to continue its losing battle, prolonging its inevitable defeat and increasing the toll of avoidable deaths.
Conversely, however, Trump has made clear he will do nothing to stop Israel's genocide in Gaza, and it is unlikely he will make any effort to rein in the horrors of that campaign. It is not clear that the Democrats were doing anything about this either, so it is not clear to me whether the genocide will proceed more rapidly or openly under Trump.
Sadly, I think we will see the extermination of the entire population of Gaza under Trump's presidency, but we should not assume this would have proceeded any differently under a different party.

Summary

Australia's prime minister Paul Keating once said "if you change the government you change the country", but in the case of the USA that principle is too narrow - when you change the US government you change the world. The Republican party has become more extreme, more ideological and more nihilistic than ever before since Trump took it over, as well as shifting to a more isolationist vision for America. For global health this will mean a withdrawal of US support for initiatives like PEPFAR, USAID development money, and cooperation agreements that have been broadly positive for global health, alongside a shift towards a domestic public health policy that is inequitable, anti-scientific and ultimately terrible for the health of Americans. The spillover from that domestic policy will potentially lead to a growth of infectious diseases and health risks globally. The US may also withdraw from global health responsibilities it has adhered to for decades, and although its contributions to global health have always been patchwork, ideologically driven and inefficient, the withdrawal of funds and cooperation that may happen under Trump will work to slow progress towards health for all, and increase global risks in a wide range of areas.
Of course it's impossible to predict the precise trajectory of government policy in the early days of a new administration, and the outcome of factional battles within the Republican party is difficult to predict. Nonetheless, all the signs point to significant setbacks for public health within the USA, and challenges to progress in health globally. At a time of unprecedented crises in global health, let us hope that other rich countries - particularly Japan and China - will step in to support continued progress on global health, and a better future of health for all.