At noon on January 20, 2021, Donald Trump’s nuclear codes went dead. Around the world, atomic experts breathed a sigh of relief.

The last weeks of the Trump administration had seen the president impeached for “incitement of insurrection” and banned from Twitter, yet he remained the only person in the U.S. with the authority to launch a nuclear attack.

It was an irony not lost on Tom Collina, director of policy at the Ploughshares Fund, a disarmament-advocacy group. “We don’t trust him with Twitter,” said Collina at the time. “And yet we trust him with nukes. It makes no sense.”

There were many who did not trust Trump with the nation’s arsenal of more than 5,400 nuclear weapons, including House Speaker Nancy Pelosi. In the aftermath of the attack on the Capitol, Pelosi referred to Trump as “crazy” and sought assurances from the Pentagon that “safeguards” were in place to prevent an “unstable president” from ordering a nuclear strike. Pelosi told the public that she had received assurances from the country’s top military officer, General Mark Milley, that such safeguards were in place should Trump decide to launch a nuclear attack in the final days of his presidency.

These weren’t just empty words. According to Bob Woodward and Robert Costa, General Milley was so concerned about Trump’s “serious mental decline” in the aftermath of the election that he took steps to limit the president from ordering an ill-judged military operation or launching nuclear weapons. Further disclosures, made to The New Yorker’s Susan B. Glasser, confirmed that Milley had instructed the Joint Chiefs not to carry out any unlawful orders without calling him first. Despite it being technically illegal to disobey an order from the commander in chief, the general reportedly reassured an anxious Pelosi and other worried members of Congress, saying, “Our loyalty is to the U.S. Constitution.”

Trump is out of office—for now. But his decision to run for the presidency in 2024 once again underlines the dangers represented by “national leaders who have sole control of the use of nuclear weapons.” At the start of 2021, the panel of international scientists responsible for setting the so-called Doomsday Clock voted to keep its time unchanged at 100 seconds to midnight. In other words, “Apocalypse Soon.”

And that was before Vladimir Putin’s bloody invasion of Ukraine. Since then the Russian president has called for his country’s nuclear forces to be placed on “high alert” and issued televised nuclear threats that have grown more strident as his country’s position on the battlefield weakens.

“Russia’s brutal war in Ukraine shows the danger of sole authority in a new light,” says Collina. “The decision to launch Russian nuclear weapons rests with one unstable leader.”

Closer to home, fears of an “unhinged” U.S. president launching a rogue nuclear strike are nothing new. During the Watergate era, Secretary of Defense James Schlesinger put in place measures (similar to those adopted by General Milley) to prevent the possibility of an increasingly unstable President Nixon from ordering a nuclear attack.

In November 2017, after Trump’s “fire and fury” spat with North Korean president Kim Jong Un, the U.S. Senate Foreign Relations Committee held its first hearing in 41 years on the president’s powers of sole authorization. Democratic senator Chris Murphy, of Connecticut, told the committee that many Americans were worried President Trump might order a nuclear strike “wildly out of step with U.S. national-security interests.”

Collina, who recently co-authored The Button: The New Nuclear Arms Race and Presidential Power from Truman to Trump with former U.S. defense secretary William J. Perry, states that “having a ‘madman’ in the White House” should be “a wake-up call to the frightening reality that when it comes to nuclear weapons, presidents have almost complete autonomy with essentially no institutional checks and balances.”

Despite it being technically illegal to disobey an order from the commander in chief, the general reportedly reassured an anxious Pelosi and other worried members of Congress, saying, “Our loyalty is to the U.S. Constitution.”

As an 18-year-old army engineer in Japan, Secretary Perry, now 95, saw firsthand the aftermath of the firebombing of Tokyo. “When I saw the devastation,” he says, “I lost all illusion of what a wonderful thing war was.” During the Cuban missile crisis, Perry analyzed C.I.A. intelligence on Soviet plans to station nuclear missiles in Cuba. “I went to work every morning believing it would be my last day on earth,” he recalls. During President Clinton’s 1997 inauguration ceremony, Perry was the so-called designated survivor—the member of the Cabinet chosen to stay at an undisclosed secure location in the event of an attack that incapacitates everyone else.

As Clinton’s secretary of defense, Perry oversaw the dismantling of more than 8,000 American and Soviet nuclear warheads. On a visit to post–Cold War Ukraine, Perry joined the Russian and Ukrainian defense ministers in the ceremonial planting of sunflowers on a former ICBM storage site 150 miles south of Kyiv. Since leaving office he has devoted his life to educating the public about the dangers of nuclear weapons.

Along with all other nine living former defense secretaries (from both Republican and Democratic administrations), Perry signed a letter printed in The Washington Post shortly before the January 6 Capitol attack, urging U.S. military personnel and Defense Department officials to remember their “solemn obligations” to the Constitution.

In a telephone call on January 14 while Trump was still in power, six nervous days away from President Biden’s inauguration, Perry, who has been described as “America’s nuclear conscience,” explained why he felt it was necessary to publish the letter at that particular moment. “I thought it had needed saying for a long time,” he said, adding, “At that moment, saying it might make a difference.”

Given what we now know about General Milley’s behind-the-scenes maneuvering in the last days of the Trump White House, it seems the letter did indeed make a difference—at the very least serving as a public show of solidarity. But in Perry’s view, subverting the chain of command is not what the military is authorized to do. Acting in this way leaves military personnel open to charges of treason, an allegation Trump has since levied against Milley. Moreover, says Perry, “we cannot be sure” the generals would disobey the president. Treason is still punishable by death, after all.

The U.S. nuclear-command system’s Personnel Reliability Program (P.R.P.), which evaluates many aspects of an individual’s professional and domestic life, stipulates: “Only those personnel who have demonstrated the highest degree of individual reliability for allegiance, trustworthiness, conduct, behavior, and responsibility shall be allowed to perform duties associated with nuclear weapons, and they shall be continuously evaluated for adherence to PRP standards.”

Breaches are rare, but they do happen. In 2013, Vice Admiral Tim Giardina, the second-highest-ranking officer at U.S. Strategic Command (STRATCOM), had his nuclear access revoked after he was caught using fake gambling chips in an Iowa casino. The counterfeiting charges were eventually dropped, but Giardina was found guilty on two counts of “conduct unbecoming an officer and a gentleman.”

That same year, Major General Michael Carey, an air-force commander with authority over U.S. intercontinental ballistic missiles, was stripped of his nuclear privileges for excessive consumption of alcohol during an official trip to Russia, generally “rude” behavior, associating with “foreign national women at the Ritz Carlton,” and repeatedly demanding to be allowed to sing onstage with a Beatles-tribute band at a Mexican restaurant near Red Square.

During the Cuban missile crisis, Perry analyzed C.I.A. intelligence on Soviet plans to station nuclear missiles in Cuba. “I went to work every morning believing it would be my last day on earth.”

Only one person with nuclear access is exempt from the continuous evaluation required by the P.R.P.: the commander in chief. In the words of General Maxwell D. Taylor, “As to those dangers arising from an irrational American president, the only protection is not to elect one.”

But all presidents are fallible and capable of instability. Kennedy took a cocktail of medications. Nixon drank. Reagan fell asleep during Cabinet meetings. And Biden is the oldest president to have taken the oath of office; if he is re-elected, he will earn that distinction a second time.

Since 1945, America’s nuclear powers have evolved in response to the threat (or perceived threat) posed by its enemies. Top-secret documents declassified in 1998 reveal that Eisenhower delegated powers of authorization in 1959 to around half a dozen high-level military commanders in “circumstances of grave necessity” if the president couldn’t be contacted. Although he worried that a hotheaded general might “do something foolish down the chain of command” (as in Stanley Kubrick’s 1964 film, Dr. Strangelove), Eisenhower believed the enemy presented a greater threat.

Ike’s secret delegation of nuclear authority came as a surprise even to Kennedy, who was equally astonished by the lack of protection over the weapons themselves. Incredibly, as detailed in Eric Schlosser’s Command and Control, few of the 3,000 American nuclear weapons stored in Europe had locks on them. In response, Kennedy tightened security, and, although many historical details remain classified, steps were taken to centralize nuclear authority within the presidency, resulting in the system the U.S. employs today. A system chillingly summed up by Nixon in 1974: “I can go back into my office and pick up the telephone and in 25 minutes 70 million people will be dead.” For Perry, a better way is clear. “The thing to do is to disestablish the president’s sole authority.”

Not everyone agrees, however. Professor Peter Feaver, director of Duke University’s Program in American Grand Strategy, believes that sole authority is “the least bad solution given the strategic reality.” While acknowledging that the counter-arguments are “serious,” he points out that many of those who now argue against sole authority did not “reform the system when they had the opportunity.” To Feaver, that “suggests that there is a powerful logic on the other side that convinced them not to.” And that, he says, is the logic of deterrence.

The U.S. and the Soviet Union were like “two scorpions in a bottle,” said J. Robert Oppenheimer, director of the Los Alamos National Laboratory, “each capable of killing the other, but only at the risk of his own life.” In Feaver’s view, sole authority is justified because it provides the best guarantee that the U.S. will always be able to launch a nuclear attack, even under the most extreme circumstances.

When asked what can be done about an “unstable” president, Feaver says, “You seek a political solution. You use the 25th Amendment or move to impeach.” Yet these measures take weeks, even months. All the president has to do to order a nuclear strike, meanwhile, is place a call to the Pentagon, verify his or her identity using the nuclear codes printed on a special card known as the “biscuit,” and specify a target from a pre-existing “menu” of strike options carried inside the “football.” That’s it: a doomsday version of room service.

Nevertheless, Feaver argues, there are safeguards. “In the nightmare scenario,” he says, “the military would not say, ‘Let missiles fly,’ they would ask questions. ‘Where’s the secretary of defense?’ ‘Let me check with my lawyers,’ etc. Yes, one man alone has the legal authority, but he relies on many, many other people to obey that order.”

Will we be so lucky when the next “madman” comes along? “We cannot assume that we will never have another president as unqualified as Trump,” Collina argued in a 2021 op-ed published on the Web site Defense One. “Nor can we assume that future generals will stand up to them.”

With Trump running again, Collina’s argument that Biden should “fix the system for himself and all future presidents” seems more pertinent than ever. “Reform of sole authority would require Biden to limit his own authority,” Collina points out, “but perhaps he will do it for the good of humanity?”

Biden ran for office on a platform opposing new nuclear weapons, and one of the first actions he undertook as president was to extend the START arms-control treaty with Russia. But confronted with Putin’s invasion of Ukraine and China’s increasing nuclear capability, the administration’s Nuclear Posture Review, released in October, opens the door to “force adjustments.” In other words, more nukes. Taking to Twitter, Collina called it “a missed opportunity.”

“We are closer to nuclear war than anytime since 1962,” he wrote.

Rebecca John is a freelance writer and award-winning documentary filmmaker