Graff: It's entirely accurate -- at least once a launch order is given.

Obviously, the aides around the President could try to talk him out of it, if they disagreed with it, but our entire system is geared towards establishing whether a launch order is "valid" only insofar as whether it's actually coming from the President of the United States. There's a classified system of code words that communicate between the President and the person executing the launch order -- either at the Pentagon or the mountain bunker in Pennsylvania, Raven Rock, that serves as the alternate Pentagon -- that the person on the other end of the phone is the actual legitimate commander in chief. But, there's no check or balance in the system about whether it's "valid" to start a nuclear war. There's no second voice, like the defense secretary or chairman of Joint Chiefs, that has to OK a launch.

As bonkers as that may seem, it's a procedure that dates back to the Cold War, when we faced the Soviet Union with tens of thousands of nuclear warheads on hair-trigger alert. A president would have only about 15 minutes to respond to an attack -- perhaps even less -- so we devoted literally billions of dollars to building a system that could transmit a launch order as quickly as possible.

From the time that a president orders a launch, the first ICBMs would leave their silos about four minutes later.

Cillizza: Let's talk nuclear Football. Who carries it? How is that person chosen? What does it look like? What does it contain?

Graff: The Football -- the nickname comes from the first nuclear war plan, code-named DROPKICK -- is a black briefcase carried by a rotating series of military aides who are never more than a few steps from the President. It's easy to forget it's there, except when you see a guest at Mar-a-Lago snap a selfie with the military aide -- but that aide is always present. When the President gets on an elevator, so does the Football. When you see the President driving his golf cart around his club, there's a golf cart right behind him with the military aide and the Football. During Jimmy Carter's presidency, when he went rafting out west, the Football was in a raft right behind him on the river.

A White House military aide and member of the US Navy carries a briefcase known as the "football," containing emergency nuclear weapon codes, as then-President Barack Obama departs from the White House in 2012.

But contrary to popular culture, the Football doesn't have some fancy retina scanner or big red button -- the only red button in Trump's life is the one on his Oval Office desk that orders a Diet Coke from the White House Mess. The Football is actually full of binders and plans for war, so that a President can flip through it and decide what kind of nuclear war he wants to launch -- then he communicates that order to the Pentagon or Raven Rock, where it's promptly executed. There's a visual guide as part of the Football that one military aide referred to as the "Denny's Menu" of nuclear war. But other aides have darkly joked there are really just three options: Rare, Medium and Well-Done.

Cillizza: Can the holder of the Football refuse to turn it over to the president? Can anyone in the chain of command do that?

Graff: Sure, he could try, but it'd be both illegal and go against all the traditions of the US military. The entire launch system is geared towards executing a unilateral launch order as quickly as possible. And the president could instantly fire and remove anyone in the chain of the command who tried to block, slow or countermand his order -- up to and including the defense secretary.

That said, we do know of one instance where this happened: During the final days of Richard Nixon's presidency, Secretary of Defense James Schlesinger quietly tried to trim the presidential launch authority. Aides were worried that Nixon was drinking heavily and (was) despondent, and they feared what he might do. He even threatened a group of congressmen that he might launch a nuclear war.

So Schlesinger later said -- and we only have his word to go on for this story -- that he told the Pentagon to double-check with him or Secretary of State Henry Kissinger first if they received a presidential launch order. Then, in the literal final hours [of Nixon's presidency], the White House actually took the Football away from Nixon. It didn't travel aboard Air Force One as Nixon began to fly home and stayed instead with the incoming commander in chief, Gerald Ford. But all of that was entirely extralegal, and there's no technical process to execute such a move.

Cillizza: How -- and could -- the protocol around the use of the nuclear codes be changed?

Graff: There's actually legislation pending on Capitol Hill right now to insert a check on the presidential launch authority. : There's actually legislation pending on Capitol Hill right now to insert a check on the presidential launch authority. Rep. Ted Lieu (D-California) and Sen. Ed Markey (D-Massachusetts) introduced legislation in January that would prohibit a president from launching a first strike without a congressional declaration of war.

What's strange too about the nuclear launch procedures is that at all other levels, there's the "two-man rule." Launching nuclear weapons in a missile silo, aboard a bomber, or aboard a submarine always requires both the commander and the number two to concur that a launch order is valid (e.g., that the code to launch is correct and authorized).

Working around nuclear weapons are always considered "No Lone Zones," where people have to work in teams of two to ensure that one person is never alone with a bomb. It seems strange that there's no similar "two-man rule" for the actual launch order. Even if you didn't want to include Congress, it would make sense for a defense secretary, vice president or chairman of the Joint Chiefs of Staff to have to concur that a president had a good reason to launch an attack.

Cillizza: Finish this sentence: "The most likely outcome if Trump called for a nuclear response to North Korea would be ________." Now, explain.

Graff: The most likely outcome if Trump called for a nuclear response to North Korea would be that nuclear missiles launched, and likely very quickly. As much as you may want to believe that (Secretary of Defense) Jim Mattis, (White House Chief of Staff) John Kelly or (National Security Adviser) H.R. McMaster has some secret plan to stop an ill-conceived strike, it's unlikely under our current system that the military chain of command would do anything other than execute the launch order as quickly as possible.

North Korea is only ever about 30 minutes away from nuclear destruction -- which, you could say, is precisely why North Korea is trying hard to rapidly build its own capability and ensure that it could deter such an attack by threatening the United States. That's the theory, after all, that kept nuclear war at bay throughout the Cold War.