It takes at least two people to launch a nuclear weapon at almost every point in the US chain of command. Missile silos, bombers, nuclear submarines – all require more than one officer to validate a “go” order.

The exception is at the top, in the Oval Office. It’s true: A president alone has the authority to push the metaphoric button and authorize use of the nation’s atomic arsenal.

Should this be the case? President Trump’s behavior in office has raised anew this old question. Critics worry that Mr. Trump’s bellicosity toward North Korea – he’s threatened to rain “fire and fury” on the Pyongyang regime – reveals a cavalier attitude toward the use of nukes. Sen. Bob Corker (R) of Tennessee, chairman of the Foreign Relations Committee, has gone so far as to say Trump may be putting the US “on the path to World War III.”

The problem is that US nuclear command-and-control was designed this way for what the US national security structure considers good reasons. It is meant to ensure political control over the military and a quick response in a crisis, the better to deter potential adversaries. Changing it might involve difficult practical and constitutional questions.

In any case, the system might be more resistant to impulsive presidential behavior than it appears on paper. While the president orders nuclear operations, that order passes through a chain of command on its way to US forces. It’s very unlikely that Trump could wake up angry, fire off tweets about an adversary, and then decide to end the argument once and for all.

“The notion that a president could capriciously launch a nuclear first strike suggests that no one in the chain of command would raise a question or intervene. In practical terms I find that hard to believe,” says Rebecca Hersman, a former deputy assistant secretary of Defense for countering weapons of mass destruction who is currently a senior advisor at the Center for Strategic and International Studies.

Military would ‘be asking all sorts of things’

If the president is awakened by a phone call in the middle of the night and has only minutes to decide whether to retaliate against an incoming adversary attack, the military would be primed to execute that order whatever it is, adds Peter Feaver, a former National Security Council staff member under President George W. Bush.

But if the communication runs the other way – if a president wakes up the military at 3 a.m. and wants to attack someone due to something he’s seen on cable news – the dynamic would be very different, says Dr. Feaver, a professor of political science at Duke University.

In that scenario the military would not be primed to respond reflexively. It would start to ask questions. Is this legal under US law? Is it legal under the laws of war? Is it really a good idea?

“They’d be asking all sorts of things. It wouldn’t be an automatic response. I’m not saying they would flat-out disobey the president. I’m saying they would raise the question,” says Feaver.

For context, he says, look at the way the Department of Defense handled Trump’s tweet that transgender troops would be banned. The Pentagon has clearly slow-walked that process and has not implemented far-reaching interpretations of that order.

A lesson from 1974

A nuclear order would be a far more immediate and dire matter, of course. But there’s evidence that in the past the military has quietly moved to lessen a pressured president’s ability to launch weapons.

While it remains unclear what exactly happened, it seems that top White House staff and military officers were on guard against sudden orders from President Nixon in his last days in the White House. Jeffrey H. Smith, former general counsel of the CIA, has recently written that as a young military lawyer in 1974 he saw a message from the chairman of the Joint Chiefs to four-star subordinate commanders. It ordered the four-stars to check with the chairman and the secretary of Defense if they received any “execute” orders from the president.

On August 9, 1974, Nixon boarded Air Force One a last time as he left the White House for good, waving and forcing a smile as his hours as president ticked away. According to the timing of his resignation he would remain chief executive for a few hours as he flew toward California. But unbeknownst to him, the nuclear “football” – the suitcase containing launch codes – was already elsewhere. It had been quietly transferred to the vicinity of his successor, Vice President Gerald Ford.

The ‘football’

The “football” is the core of a president’s nuclear power. It contains devices enabling the chief executive to authenticate his identity and a short menu of different mixes of weapon launches from which they can choose.

It is the center of a system designed for three things: to prevent anyone but a president from directing nuclear use, to ensure reliability in a crisis, and to be fast.

The point is for every possible adversary to know that they can’t decapitate the US government with a quick first strike and win a nuclear exchange. No matter what, their country will be destroyed if they try.

“Much of the US nuclear command and control system was developed to be able to withstand the most awful of circumstances ... to ensure a lawful order could be issued even if the US was already under a nuclear attack,” says Ms. Hersman.

However, it’s asking a lot of any human to give them such awesome life-and-death power, alone. Trump may seem impulsive, but other chief executives have had flaws. John F. Kennedy suffered health problems and took powerful medications. Nixon drank under pressure.

Pelosi calls for a new system

House Minority Leader Nancy Pelosi last week said it was “urgent” to design a better system. Perhaps Congress should pass law banning the US from first use of nuclear weapons, she said. Another approach might be to require a president to discuss any nuclear use with cabinet members.

“I believe that if we go forward with anything like that it has to be in a bipartisan way, because it’s about all presidents. No matter who he or she may be down the road,” said Representative Pelosi.

But restrictions on a president’s ability to use force could run smack into the Constitution’s recognition of the president as commander-in-chief. And there would be practical considerations – would a ban on first use complicate the ability of the US to preempt an imminent attack?

It is in the gray area between responding to an identifiable attack and a clear US first strike that there are difficult questions of law and politics. Consider this scenario: A president and his cabinet have been through a deliberative process for months about an adversary attempting to arm itself with nuclear weapons. Sanctions and threats have run their course. It’s time to just preempt them with US nuclear missiles, says the president. Yet many military officials and some cabinet members aren’t convinced.

If the president persists, the military has to go along. It’s true that in such a dispute the White House wins, in terms of the law.

But the bureaucracy has its own weapons. It could leak, copiously. Top officials could resign. It is easy to see how such a situation could create a national political uproar.

To some extent, there already is a two-man rule at the top of the nuclear pyramid, says Peter Feaver. Any authenticated nuclear order must pass through the secretary of Defense, the next link down from the president in the National Command Authority. The White House does not communicate directly with missile silos or bombers. Pointing that out publicly might be a good thing.

“You are just clarifying for a worried public that is the case,” Feaver says.