Wednesday morning, NBC’s Joe Scarborough said something profoundly frightening about Donald Trump. In a private conversation with a foreign policy expert, Scarborough reported, Trump asked — repeatedly — why we have nuclear weapons if we don’t use them.

"Several months ago, a foreign policy expert on the international level went to advise Donald Trump. And three times [Trump] asked about the use of nuclear weapons. Three times he asked at one point if we had them why can't we use them," Scarborough said.

Obviously, this isn’t gospel; it’s a thirdhand report of a conversation that may or may not have happened. But it tracks with what Trump has said publicly. When MSNBC’s Chris Matthews told Trump in March that presidents shouldn’t suggest they might use nukes, as Trump has done repeatedly, the candidate responded with a question: "Then why do we make them?"

This raises some very, very scary questions about Trump’s judgment. It suggests that he doesn’t know the basic way nuclear weapons are supposed to work — deterring attacks on the United States — and that he might be the first president since Harry Truman to order the use of nuclear weapons.

The natural question to ask, then, is whether he could actually do that. The answer is deceptively simple: Yes, he can. No matter what.

The president has basically unconstrained authority to use nuclear weapons, a seemingly insane system that flows pretty logically from America’s strategic doctrine on nuclear weapons. The US needs a system to launch weapons fast for deterrence to work properly, which means one person needs to be able to order the use of nukes basically unencumbered. The president is the only possible choice.

This entire system, however, is built around a basic faith in democracy: that the American people will elect a sober, stable leader who understands the seriousness of nuclear weapons. Someone not named Donald Trump.

No one could stop President Trump from using nukes

In 2008, then–Vice President Dick Cheney said something pretty chilling about nuclear weapons during a Fox News appearance. According to Cheney, the president is always accompanied by a military aide carrying a briefcase, called the "nuclear football," which allows the president to launch nuclear weapons. The president can launch at whomever, whenever:

He could launch a kind of devastating attack the world's never seen. He doesn't have to check with anybody. He doesn't have to call the Congress. He doesn't have to check with the courts. He has that authority because of the nature of the world we live in.

This may sound like Cheneyian hyperbole. But Ron Rosenbaum, a journalist who wrote a book about America’s nuclear weapons, looked into Cheney’s claims as part of a 2011 Slate piece. He concluded that they were basically accurate.

"No one could come up with a definitive constitutional refutation of this," Rosenbaum writes. "Any president could, on his own, leave a room, and in 25 minutes, 70 million (or more than that) would be dead."

Now, there’s a slight wrinkle: The secretary of defense is required to verify the president’s order to launch. But he or she doesn’t have veto power. If the president orders a nuclear launch, the secretary is legally obligated to do it. He or she could theoretically choose to resign rather than carry out the order, but then it would fall to the secretary’s second-in-command to order the strike.

"It's up to the president," Kingston Reif, the director for disarmament and threat reduction policy at the Arms Control Association, tells me. "The advisers that make up the national command authority are obliged to obey and execute the order."

President Donald Trump could order a nuclear strike about as easily as you or I could order a Grand Slam breakfast

This may sound insane. But to understand why it works this way, you need to understand a little about how the US government thinks about nuclear weapons.

America’s nuclear system has been designed with an eye toward MAD — mutually assured destruction. That’s the idea that no country would nuke the United States first if it knew America would be able to launch a devastating response. Every US nuclear system is thus designed around establishing deterrence: making sure other countries can be certain that the US will be able to nuke them back no matter what.

The US being able to launch fast is a key part of this system. It takes roughly 30 minutes for a nuclear missile to travel between Russia and the United States; Moscow needs to know that the US can respond before then. Otherwise, it might be tempted to nuke Washington in an attempt to destroy the US government before anyone could order retaliation.

Hence why the system has no formal checks on the president’s authority to order nukes. Serious constraints would, according to standard nuclear deterrence theory, make a nuclear attack more likely.

At the same time, you also don’t want a rogue military officer going off and launching nukes on his own. You need a system that allows the president to launch nuclear weapons quickly, but also one that ensures the launcher has proper identification and that it is nuking the right countries (you don’t want to hit China if Russia is the actual one launching nukes).

The nuclear football system, developed as a result of the Cuban Missile Crisis, is a way to accomplish both goals. The football is designed to verify the president’s identity — using a code card, called "the Biscuit," that the president carries at all times — while also allowing for near-immediate nuclear launch potential. Scientific American’s Michael Dobbs explains how:

Contrary to popular belief, the Football does not actually contain a big red button for launching a nuclear war. Its primary purpose is to confirm the president’s identity, and it allows him to communicate with the National Military Command Center in the Pentagon, which monitors worldwide nuclear threats and can order an instant response. The Football also provides the commander in chief with a simplified menu of nuclear strike options — allowing him to decide, for example, whether to destroy all of America’s enemies in one fell swoop or to limit himself to obliterating only Moscow or Pyongyang or Beijing.

Dobbs, a former military aide to President Clinton, described the targeting options as a "Denny’s breakfast menu," allowing presidents to pick "one [target] out of Column A and two out of Column B."

A few ISIS-held cities here, a few Chinese nuclear silos there: President Donald Trump could order a nuclear strike about as easily as you or I could order a Grand Slam breakfast.

Why presidents don’t use nukes — but Trump might

You might think this system would be incredibly destabilizing — that leaders of other countries might have been terrified about a US president deciding that nukes are a simple way to solve a hard policy problem.

But it hasn’t been. There’s a reason for that, going back to World War II — one that Trump might not fully appreciate.

After Harry Truman used the bomb on the Japanese cities of Hiroshima and Nagasaki, the horrific consequences of nuclear use became abundantly clear. Truman himself came to believe that the US should never use nuclear weapons as ordinary weapons of war. He refused to use them in the Korean War, even when China’s entry turned the tide against America, for this reason.

"You have got to understand that this isn’t a military weapon," Truman said in April 1948. "It is used to wipe out women and children and unarmed people, and not for military uses. So we have got to treat this differently from rifles and cannon and ordinary things like that."

Truman’s apprehension became widely shared, helping create something scholars now call the "nuclear taboo."

The US and other world powers don’t see nuclear weapons simply as bigger bombs. They see them as qualitatively different from conventional weapons: something that cannot be used in the ordinary course of war. No one talked about America using nukes during the Iraq War or Russia using nukes against Chechen rebels, because the very idea of using such a destructive weapon under such mundane circumstances is unthinkable.

"A powerful taboo against the use of nuclear weapons has developed in the global system, which, although not (yet) a fully robust prohibition, has stigmatized nuclear weapons as unacceptable weapons," Nina Tannenwald, a professor of international relations at Brown University, writes in her groundbreaking book on the taboo. "The effect of this taboo has been to delegitimize nuclear weapons as weapons of war."

Presidents since Truman have, to varying degrees, accepted this norm. While US nuclear doctrine doesn’t formally rule out the offensive use of nuclear weapons, it’s basically understood that a president wouldn’t consider using nukes unless America had somehow gotten involved in a shooting war with a nuclear power, like Russia or China, and that things would have to have gone very wrong.

This is because past US presidents have appreciated the seriousness of nuclear weapons. Say what you will about either George W. Bush or Barack Obama, but their foreign policy ideas and advisers all came from basically mainstream traditions that understood the reasons the US doesn’t use nukes as a matter of course. Ditto Bill Clinton, George H.W. Bush, and on down the line.

Trump, by contrast, has basically no understanding of foreign policy. His ideas are a wacko, instinctive melange, ranging from breaking up American alliances to colonizing Iraq for its oil. There’s no guarantee he understands why the United States has traditionally seen nuclear weapons as deterrents, to be used only under the rarest of circumstances.

His comments on nuclear weapons, specifically, give little reason for us to trust him. At a December Republican debate, radio host Hugh Hewitt asked him about the "nuclear triad" — the three different ways the US can deliver nuclear weapons (bomber aircraft, submarines, and land-based missiles). Here’s what Trump said:

Well, first of all, I think we need somebody absolutely that we can trust, who is totally responsible, who really knows what he or she is doing. That is so powerful and so important. And one of the things that I'm frankly most proud of is that in 2003, 2004, I was totally against going into Iraq because you're going to destabilize the Middle East. I called it. I called it very strongly. And it was very important. But we have to be extremely vigilant and extremely careful when it comes to nuclear. Nuclear changes the whole ball game. Frankly, I would have said get out of Syria; get out—if we didn't have the power of weaponry today. The power is so massive that we can't just leave areas that 50 years ago or 75 years ago we wouldn't care. It was hand-to-hand combat. The biggest problem this world has today is not President Obama with global warming, which is inconceivable, this is what he's saying. The biggest problem we have is nuclear—nuclear proliferation and having some maniac, having some madman go out and get a nuclear weapon. That's in my opinion, that is the single biggest problem that our country faces right now.

It’s not clear, in this mostly incoherent answer, that Trump actually knows what the triad is. When Hewitt pressed him, Trump answered with a single line: "I think, for me, nuclear is just the power, the devastation is very important to me."

Clearly, Trump doesn’t know the most basic thing about nuclear weapons — how the United States can launch them. This level of ignorance about the literal facts of nuclear weapons, together with his generally uneducated approach to policy, means it’s very likely he also doesn’t understand the strategic role of nuclear weapons.

Trump might order the use of nuclear weapons against ISIS — indeed, he has refused to rule it out in interviews — just because he has promised to wipe out the terrorist threat. We cannot know that he takes nuclear weapons as seriously he should.

The other reason for concern is his character.

After the Watergate scandal broke, and President Nixon became increasingly embattled politically, he turned to drink as a source of comfort. This freaked out Secretary of Defense James Schlesinger, who worried that an erratic, drunk Nixon might order a nuclear launch out of pique. Schlesinger told aides in the Pentagon war room to check with him if Nixon started talking to them about launching nukes.

Thankfully, Nixon didn’t do it. But the worry with Trump is similar: His character is so erratic that he might order a nuclear launch just because he’s mad at someone.

Think of all the bizarre feuds Trump has gotten himself into: Ghazala Khan, random fire marshals, a woman with a baby at his rally, the "short-fingered vulgarian" incident. In all of them, he has displayed a similar pattern: irrational overreaction to perceived insults and slights.

Now imagine that same tendency to overreact to insults, only with Trump’s finger on the nuclear button. Would he order a nuclear strike on a country merely because he felt its leader had disrespected him?

I hope not. But the truth is that we don’t know — which makes every stray Trump comment about nukes, even thinly sourced speculation like Scarborough’s, deeply terrifying.

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