On January 20, the military officer carrying the commands and controls for the nation’s massive nuclear arsenal—the officer who follows the president everywhere, the officer who is required to stay within a few feet of the president, required to be in the same elevator with him even as other dignitaries wait for the next cab—that officer will follow President Barack Obama to the inauguration stand on the west front of the Capitol. When he leaves, he will be following President Donald Trump.

The man who can be baited with a tweet, the man whose campaign team did not trust with a Twitter account, the man whose unpredictability and wild temperament made him an unacceptable choice for the majority of voters this November, will have, from that moment forward, the unfettered ability to launch nuclear war.

This frightens me. It frightens my 92-year-old mother-in-law, who told me, “I’m afraid that crazy man is just going to push the button!” If he did, there would be no one to stop him, short of a mutiny. There is no institutional check on a president’s ability to fire nuclear weapons should he or she wish to do so. President Trump will be able to launch, within minutes, one or one thousand nuclear weapons without any vote, any check, or even any serious deliberation.

It is one of three great nuclear risks of the Trump presidency—and one that President Obama could negate with the stroke of a pen. Before he leaves office, he could, at long last, take our nuclear weapons off hair-trigger alert. It would then take many hours, even days, to launch, allowing for consultation and reflection.

It may even be that President Trump will take steps to reduce nuclear dangers. But he first must avoid two other risky policies he favored during the campaign. He should not do anything to encourage other nations to get nuclear weapons. Trump said in election interviews that he thought it fine if South Korea or Japan or Saudi Arabia wanted nuclear bombs, because “it’s going to happen anyway.” There are already far-right, nationalist groups in South Korea and Japan pushing for nuclear weapons, and both nations have the technical capability to build them. Japan already has the plutonium needed for the cores of weapons; it could likely build a bomb within a few months.

Encouraging allies to go nuclear would reverse 71 years of American policy. No president, Democratic or Republican, liberal or conservative, has ever encouraged an ally to build nuclear weapons. Not the United Kingdom, not France, not Israel. The bedrock of US policy has been to stop the spread of these weapons and reduce the existing arsenals, working toward their complete elimination. Trump could destroy that consensus, unleashing a new, destabilizing wave of proliferation.

Trump might also rip up the historic Iran agreement or allow Congress to pass new sanctions that would violate the accord. The far-right congressional opponents of the deal are itching to do so. Trump has taken contradictory positions on the agreement, vowing to AIPAC earlier this year that he would “dismantle” it, but also saying elsewhere that he would resolutely enforce it and also that he would “review” it. 

Destroying the agreement, whether by abrogation or violation or neglect, would result in the worst of all worlds: the collapse of the sanctions regime as our allies desert us, and the collapse of any restraints on Iran’s nuclear program as the deal dissolves. We would be back on a dangerous path to another conflict in the Middle East or a nuclear-armed Iran. Or both.

Fittingly for the deeply contradictory nature of the Trump presidency, there are also three possible positive nuclear outcomes. If we can avoid the worst, it is possible that President Trump could significantly improve global nuclear security.

It is clear that Trump does not see Russia as an adversary. This may be naive, but it is possible that he, like previous Republican presidents, could agree on deep cuts in Russian and US nuclear arsenals. Indeed, it is only Republican presidents who have had the political space to make significant reductions. Ronald Reagan, George H.W. Bush, and George W. Bush made deep cuts in the arsenal, while Bill Clinton and Barack Obama just trimmed the stockpile.

This would be fairly easy for Trump to do. He and Russian President Vladimir Putin could simply agree to modify and extend the existing New Start treaty, lowering the number of weapons each side is permitted. This could mean that Trump (and Putin) could cancel some of the expensive, unnecessary new nuclear weapons both countries are building. It could also lead to Trump canceling any further deployments of anti-missile interceptors in Eastern Europe, which are no longer needed now that the Iran nuclear program has been halted—and which Russia believes are actually aimed at it.

Trump has also said that he’s willing to talk to North Korean leader Kim Jong-un. This could be a complete disaster. But, if done right, it could be a breakthrough for nuclear security, capping that growing nuclear program. There are plenty of Republican negotiators, knowledgeable and experienced with the North Koreans, who could help Trump strike such a deal. If he taps them, instead of some of the extremists he seems ready to bring into his administration, he could achieve a victory that eluded both the Bush and Obama administrations and resolve the world’s last great nuclear proliferation challenge.

Trump could even decide that the Iran agreement is actually in America’s security interest, thus ending the partisan debate on this essential accord. He will find that the military and intelligence establishments in America, Europe, and Israel believe that, as Israel Defense Forces Chief of Staff Gen. Gadi Eizenkot said, the accord “is a strategic turning point.” This would lock in an agreement that shrink-wraps Iran’s nuclear program, blocking all pathways to a bomb for at least 15 years and giving us time to develop new approaches to extend those restraints before they expire.

There is no shortage of good ideas for Trump to draw on. One source is a new report that Ploughshares Fund released this week at a special event in Washington, “Ten Big Nuclear Ideas for the Next President.” It has groundbreaking essays from Senator Dianne Feinstein, former Secretary of Defense William Perry, Senator Ed Markey, Representative Adam Smith, former CIA operative Valerie Plame, and the former commander of our nuclear arsenal, retired Gen. James Cartwright, among others. 

All agree that nuclear weapons are vastly overvalued in US defense policy, with missions they cannot achieve and budgets they do not deserve. These weapons do not address the highest-priority threats we face, such as Middle East conflicts, terrorism, and cyber-attacks. The Trump administration could achieve major national-security and economic victories in its first year by heeding some of their advice.

There are just too many unknowns to allow any reasonable prediction of what Trump may or may not do once he is in the Oval Office. We do not know which, if any, of these three great risks or three possible opportunities will develop. But the opportunity to make this world a safer place is still within reach.

A great deal depends on what we, outside of this new administration, do.