Before President Barack Obama leaves the White House, he could close a particularly dangerous door he left open – and fulfill a campaign pledge.

Obama will give his farewell address Tuesday and there is no indication that he will say anything of significance on nuclear policy. On Wednesday, Vice President Joe Biden will give a speech in Washington announcing some modest changes to our nuclear posture. Biden will almost certainly be drowned out by the surge of nomination hearings, Senate budget votes and President-elect Donald Trump’s expected press conference that same day.

Unlike Trump, neither man is prone to big statements and bold actions. In these last weeks, both are hesitant to do something on national security that would “box in” the new president.

Here’s why they should.

As soon as Trump is sworn into office on January 20, a military officer will start to follow him everywhere he goes. He will sit just outside the Oval Office while Trump works and just outside his bedroom while Trump sleeps and tweets. He will travel with him to Mar-a-Lago, and up to Trump Tower. When he gets into an elevator, the officer will squeeze in beside him.

This officer carries a briefcase with the command codes to America’s nuclear arsenal. It is the most efficient instrument of mass death ever invented.

The president is the only one allowed to use the commands in the briefcase, the only one with the unfettered ability to launch one or one thousand nuclear warheads whenever he pleases. Four minutes after he gives the order, the missiles will fly. No one can stop him, short of a full-scale mutiny. Once launched, the missiles cannot be recalled.

This nuclear posture is called high alert, or launch-on-warning, or, more commonly, hair-trigger alert. It is a vestige of the Cold War. Nuclear commanders wanted the ability to launch their land-based missiles before an enemy salvo could destroy them. For decades, experts have warned that this was a dangerous practice, subject to false alarms, mistakes, misunderstanding and human error.

Of the some 4,500 nuclear warheads in our active nuclear stockpile, about 1,000 are kept on hair-trigger alert. Each is many times the size of the bombs we dropped on Japan. Together, they can explode the equivalent of 22,000 Hiroshima’s on cities all over the planet. In just 30 minutes, they could destroy all that human civilization has created over the millennia.

There is no military reason for this overkill capability. The thousands of other nuclear weapons on our subs and bombers are not vulnerable to surprise attack. Even if all our silo-based missiles were destroyed or rendered inoperable, we would still have more than enough weapons to deter an attack or respond to one.

A previously classified study by the Department of Defense (DOD) concluded that even if Russia launched a “decapitating” first strike – a scenario DOD said “will most likely not occur” – we had the assured ability to retaliate against scores of high-value Russian targets, precisely because we have so many weapons securely based on submarines at sea.

Obama knows this system is crazy. While running for the presidency in 2008, he said this posture was “a dangerous relic of the Cold War” and promised to “address this dangerous situation.”

Bush, too, knew it was crazy. In 2000, he called it “another unnecessary vestige of Cold War confrontation” and pledged to end the “unacceptable risks of accidental or unauthorized launch.”

Once in office, however, Bush did not change this obsolete posture. Neither did Obama. Both ran into the formidable bureaucratic resistance that comes from the people with vested financial, political or institutional interest in keeping the force just the way it is. Many of the very people they appointed to implement needed reforms sided with the nuclear bureaucracy to stop them.

Here is the really bad news: Russia keeps an equally large force on high alert – and their early warning systems have deteriorated so badly that in 1995 they mistook a Norwegian weather rocket for a US submarine-launched nuclear missile and almost launched their weapons in response. We came within five minutes of the end of the world.

The entire system is insane. “These current alert levels…are sustained by a circular (though flawed) logic, whereby US nuclear forces are maintained on alert because Russian nuclear forces are on alert, and vice versa for Russian forces,” nuclear experts Hans Kristensen and Matthew McKinzie wrote several years ago. “Put another way, if nuclear forces were not on alert, there would be no requirement to keep nuclear forces on alert.”

This alert status is the main reason so many security and political leaders felt, as Sen. Marco Rubio said, we simply could not give “the nuclear codes of the United States to an erratic individual.” Obama, himself, has repeatedly and publically expressed his lack of confidence in Trump’s temperament and fitness for the presidency. POLITICO reported January 3, “President Barack Obama still doesn’t think Donald can handle the nuclear codes or safely protect America from attack – he just doesn’t want to talk about it anymore.”

He doesn’t have to talk about it. With the stroke of a pen, Obama can take our nuclear missiles off hair-trigger alert before he leaves office. He can close the door to an impetuous, ill-considered nuclear war. Scores of leading nuclear scientists wrote to him last June asking him to do so. The foundation I lead, Ploughshares Fund, just launched a new public petition to do it now, before the end of his term. We will present the petition to the President on January 10.

Yes, Obama’s far-right critics will denounce him. Yes, Cold War hawks in both parties will criticize him. But the majority of the American public will cheer the news and many in the military will breath a sigh of relief.

Our petition has garnered almost 90,000 signatures within a few days. It is one of the most popular petitions about nuclear weapons on Change.org. The most popular is a plea to abolish nuclear weapons. But it took that group two years to get 200,000 signatures. We reached our goal in two weeks.

Still, why bother with an executive order, even if it would be popular? Trump could theoretically reverse it once in the Oval Office. But this will be hard to do politically. It would be seen as raising tensions; he would have to explain what justified putting our nuclear missiles on high alert.

More importantly, Trump may not approve of this nuclear posture at all.

One of the core issues in Trump’s foreign policy has been his desire for improved relations with Russia. If Obama doesn’t take nuclear missile off Cold War alert, Trump likely will. It would be a logical part of reducing tensions between the two nations, lowering global nuclear risks, and marking a dramatic beginning to the Trump Era. And it is completely within a president’s authority to do so. No Congressional approval is needed.

Trump could still launch nuclear weapons in an emergency, but it would take hours or days. This gives time for consultations, deliberation, time to check mistakes and blunt the impulses of the moment. More time doesn't weaken our national security; it strengthens it.

As we argue in our petition, “Taking this critical step would bring profound security benefits for all Americans by reducing the risk of nuclear disaster.” While it won’t cut any weapons, it will make us all substantially safer.

When president, Trump will still get the keys to the arsenal, but Obama should at least lock the nuclear door before he leaves.

Joe Cirincione is president of Ploughshares Fund, a global security foundation.

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