In 1987, Donald Trump said he had an aggressive plan for the United States to partner with the Soviet Union on nuclear non-proliferation. He was motivated by, among other things, an encounter with Libyan dictator Muammar Qaddafi’s former pilot, who convinced him that at least some world leaders are too unstable to ever be trusted with nuclear weapons. Now, 30 years later, Trump—following a presidential campaign marked by impulsive, combative behavior—seems poised to become one of those unstable world leaders.

Global catastrophic risks are those that threaten the survival of human civilization. Of all the implications a Trump presidency has for global catastrophic risk—and there are many—the prospect of him ordering the launch of the massive US nuclear arsenal is by far the most worrisome. In the United States, the president has sole authority to launch atomic weapons. As Bruce Blair recently argued in Politico, Trump’s tendency toward erratic behavior, combined with a mix of difficult geopolitical challenges ahead, mean the probability of a nuclear launch order will be unusually high.

If Trump orders an unwarranted launch, then the only thing that could stop it would be disobedience by launch personnel—though even this might not suffice, since the president could simply replace them. Such disobedience has precedent, most notably in Vasili Arkhipov, the Soviet submarine officer who refused to authorize a nuclear launch during the Cuban Missile Crisis; Stanislav Petrov, the Soviet officer who refused to relay a warning (which turned out to be a false alarm) of incoming US missiles; and James Schlesinger, the US defense secretary under President Richard Nixon, who reportedly told Pentagon aides to check with him first if Nixon began talking about launching nuclear weapons. Both Arkhipov and Petrov are now celebrated as heroes for saving the world. Perhaps Schlesinger should be too, though his story has been questioned. US personnel involved in nuclear weapons operations should take note of these tales and reflect on how they might act in a nuclear crisis.

Risks and opportunities abroad. Aside from planning to either persuade or disobey the president, the only way to avoid nuclear war is to try to avoid the sorts of crises that can prompt nuclear launch. China and Russia, which both have large arsenals of long-range nuclear weapons and tense relationships with the United States, are the primary candidates for a nuclear conflagration with Washington. Already, Trump has increased tensions with China by taking a phone call from Taiwanese President Tsai Ing-wen. China-Taiwan relations are very fragile, and this sort of disruption could lead to a war that would drag in the United States.

Meanwhile, Trump’s presidency could create some interesting opportunities to improve US relations with Russia. The United States has long been too dismissive of Moscow’s very legitimate security concerns regarding NATO expansion, missile defense, and other encroachments. In stark defiance of US political convention, Trump speaks fondly of Russian President Vladimir Putin, an authoritarian leader, and expresses little interest in supporting NATO allies. The authoritarianism is a problem, but Trump’s unconventional friendliness nonetheless offers a valuable opportunity to rethink US-Russia relations for the better.

On the other hand, conciliatory overtures toward Russia could backfire. Without US pressure, Russia could become aggressive, perhaps invading the Baltic states. Russia might gamble that NATO wouldn’t fight back, but if it was wrong, such an invasion could lead to nuclear war. Additionally, Trump’s pro-Russia stance could mean that Putin would no longer be able to use anti-Americanism to shore up domestic support, which could lead to a dangerous political crisis. If Putin fears a loss of power, he could turn to more aggressive military action in hopes of bolstering his support. And if he were to lose power, particularly in a coup, there is no telling what would happen to one of the world’s two largest nuclear arsenals. The best approach for the United States is to rethink Russia-US relations while avoiding the sorts of military and political crises that could escalate to nuclear war.

The war at home. Trump has been accused many times of authoritarian tendencies, not least due to his praise for Putin. He also frequently defies democratic norms and institutions, for instance by encouraging violence against opposition protesters during his presidential campaign, and now via his business holdings, which create a real prospect he may violate the Constitution’s rule against accepting foreign bribes. Already, there are signs that Trump is profiting from his newfound political position, for example with an end to project delays on a Trump Tower in Buenos Aires. The US Constitution explicitly forbids the president from receiving foreign gifts, known as “emoluments.”

What if, under President Trump, the US government itself becomes authoritarian? Such an outcome might seem unfathomable, and to be sure, achieving authoritarian control would not be as easy for Trump as starting a nuclear war. It would require compliance from a much larger portion of government personnel and the public—compliance that cannot be taken for granted. Already, government officials are discussing how best to resist illegal and unethical moves from the inside, and citizens are circulating expert advice on how to thwart creeping authoritarianism.

But the president-elect will take office at a time in which support for democracy may be declining in the United States and other Western countries, as measured by survey data. And polling shows that his supporters were more likely to have authoritarian inclinations than supporters of other Republican or Democratic primary candidates. Moreover, his supporters cheered some of his clearly authoritarian suggestions, like creating a registry for Muslims and implying that through force of his own personality, he would achieve results where normal elected officials fail.

An authoritarian US government would be a devastating force. In theory, dictatorships can be benevolent, but throughout history, they have been responsible for some of the largest human tragedies, with tens of millions dying due to their own governments in the Stalinist Soviet Union, Nazi Germany, and Maoist China. Thanks to the miracles of modern technology, an authoritarian United States could wield overwhelming military and intelligence capabilities to even more disastrous effect.

Return to an old world order. Trump has suggested he might pull the United States back from the post-World War II international order it helped build and appears to favor a pre-World War II isolationist mercantilism that would have the United States look out for its unenlightened self-interest and nothing more. This would mean retreating from alliances and attempts to promote democracy abroad, and an embrace of economic protectionism at home.

Such a retreat from globalization would have important implications for catastrophic risk. The post-World War II international system has proved remarkably stable and peaceful. Returning to the pre-World War II system risks putting the world on course for another major war, this time with deadlier weapons. International cooperation is also essential for addressing global issues like climate change, infectious disease outbreaks, arms control, and the safe management of emerging technologies.

On the other hand, the globalized economy can be fragile. Shocks in one place can cascade around the world, and a bad enough shock could collapse the whole system, leaving behind few communities that are able to support themselves. Globalization can also bring dangerous concentrations of wealth and power. Nevertheless, complete rejection of globalization would be a dangerous mistake.

Playing with climate dangers. Climate change will not wipe out human populations as quickly as a nuclear bomb would, but it is wreaking slow-motion havoc that could ultimately be just as devastating. Trump has been all over the map on the subject, variously supporting action to reduce emissions and calling global warming a hoax. On December 5th he met with environmental activist and former vice president Al Gore, giving some cause for hope, but later the same week said he would appoint Oklahoma Attorney General Scott Pruitt, who denies the science of climate change, to lead the Environmental Protection Agency. Trump’s energy plan calls for energy independence with development of both fossil fuels and renewables, as well as less environmental regulation. If his energy policy puts more greenhouse gas into the atmosphere—as it may by increasing fossil fuel consumption—it will increase global catastrophic risk.

For all global catastrophic risks, it is important to remember that the US president is hardly the only important actor. Trump’s election shifts the landscape of risks and opportunities, but does not change the fact that each of us can help keep humanity safe. His election also offers an important reminder that outlier events sometimes happen. Just because election-winning politicians have been of a particular mold in the past, doesn’t mean the same kind of leaders will continue to win. Likewise, just because we have avoided global catastrophe so far doesn’t mean we will continue to do so.

The views in this article are the author’s alone and not those of the Global Catastrophic Risk Institute.