A system of checks and balances exists at every level of the federal government, but the dawn of the nuclear age in the mid-1940s gave the president the extraordinary power to be able to order a nuclear strike unilaterally.
Concerns over a nuclear strike once relegated to the Cold War are now back at bear the top of the national conversation as new nuclear threats, like North Korea, continue to grow, while old ones, like Russia, are starting to return. Trump has threatened "fire" and "fury" against U.S. adversaries before, but can he actually order a nuclear strike by himself?
The Nuclear Energy Act of 1947 placed the authority squarely in the hands of the president. At the time, it wasn't the whims of the executive that lawmakers were concerned about, it was generals with an itchy trigger finger who might use the world's most devastating weapons to cause an international disaster.
"The people who set up the current command-and-control system did believe there was a check in place: elections," noted Alex Wallerstein, a nuclear weapons historian at the Stevens Institute of Technology in a piece for the Washington Post in 2016. "Don’t want an insane president to have nuclear weapons? Don’t put one in office."
Of course, the implementation of a nuclear strike is a bit more complicated. Here's how it would work in theory: the president decides to order a nuclear attack, from either the "nuclear football" or another command center. The Secretary of Defense would then be responsible for relaying that order to the military. Depending on what kind of strike is ordered, the two launch officers would validate the order and "turn their keys," so to speak, thus releasing their nuclear payloads.
Nuclear launch officers are expected to simply carry out the order, no more, no less. That being said, they are also expected to follow only lawful orders.
"I provide advice to the president, he will tell me what to do and if it's illegal, guess what's going to happen. I'm going to say, 'Mr President, that's illegal'. And guess what he's going to do? He's going to say, 'What would be legal?' And we'll come up with options with a mix of capabilities to respond to whatever the situation is, and that's the way it works. It's not that complicated," said Air Force Gen. John Hyten, commander of U.S. Strategic Command, during a panel discussion at the Halifax International Security Forum on Saturday.
Military personnel are sworn to only uphold the law of armed conflict. Part of that law involves proportionality.
"Loss of life and damage to property incidental to attacks must not be excessive in relation to the concrete and direct military advantage expected to be gained," according to the U.S. Army Field Manual.
That means a nuclear strike order would theoretically have to follow the rule of proportionality to be lawful.
"I think it's important to remember that the United States military doesn't blindly follow orders," Air Force Gen. (ret.) Robert Kehler, former head of U.S. Strategic Command, told the Senate last week. "A presidential order to employ U.S. nuclear weapons must be legal. The basic legal principles of military necessity distinction and proportionality applied to nuclear weapons just as they do to every other weapon."
That said, a military officer disobeys an order on legal grounds at his own peril. Military courts don't often agree wit the subordinate who disobeys on legal grounds. But an officer who commits war crimes or other illegal actions carrying out an illegal order is still held liable for their crimes. Several members of Germany's Nazi regime attempted to defend their heinous actions by claiming they were "just following orders," but that didn't stop many of them from being hung from the gallows. The so-called "Nuremberg Defense" isn't considered legitimate.
It's possible an unwarranted, disproportionate nuclear strike could also be an illegal order. That's why, as Hyten noted, military officers train regularly to help them determine the proper course of action, should the time ever come.