Washington (CNN) President Donald Trump warned North Korean leader Kim Jong Un on Tuesday that he has a nuclear "button" on his desk at all times and boasted that the US has "much bigger & more powerful" nuclear weapons -- a stunning threat that has once again raised questions over what it takes to actually launch a nuclear warhead.
"North Korean Leader Kim Jong Un just stated that the 'Nuclear Button is on his desk at all times.' Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!" Trump tweeted.
The image of the President with his finger on a "button" that is capable of initiating a nuclear strike has been used to symbolize the speed at which the process of such an order can be carried out for decades.
Contrary to popular belief, the "nuclear football" which always accompanies a President does not contain a button but instead has the equipment and the decision-making papers that Trump would use to authenticate his orders and launch a strike.
"The President by himself cannot press a button and cause missiles to fly. He can only give an authenticated order which others would follow and then missiles would fly," Dr. Peter Feaver, a professor of public policy and political science at Duke University, told congressional lawmakers last year.
"The system is not a button that the President can accidentally lean on against the desk and immediately cause missiles to fly as some people in the public, I think, fear it would be," Feaver testified.
He added that the decision to launch a strike requires the President to work with military aides possessing the materials he needs to order an attack, as well as personnel at all levels, from top commanders all the way down to service members working in the missile silos.
Whether he is at the White House, in a motorcade, aboard Air Force One or on a trip overseas, Trump is never more than an arm's reach away as the aide carrying the football rides in the same elevator, stays on the same hotel floor and is protected by the same Secret Service agents.
There is also a football for the vice president in case the President is incapacitated.
The Presidential Emergency Satchel, as it is formally called, contains four things, according to former White House Military Office Director Bill Gulley's book "Breaking Cover."
There is a black book listing a menu of strike options; a three-by-five-inch card with authentication codes for the President to confirm his identity; a list of secure bunkers where the President can be sheltered; and instructions for using the Emergency Broadcast System.
While the military officers who would carry out a nuclear launch are required to work in pairs, where both must concur before they can execute a nuclear launch, there is no such check on the President's actions.
"Only the President of the United States can order the employment of US nuclear weapons," according to retired Air Force Gen. Robert Kehler, who testified before congressional lawmakers last year.
Much of the nuclear launch process is classified but Kehler, who previously served as the commander of US Strategic Command under President Barack Obama, explained that there are layers of safeguards within the current system designed to ensure any order is both legal and proportionally appropriate.
"This is a system controlled by human beings ... nothing happens automatically," he said, adding that the US military does not blindly follow orders and a presidential order to employ nuclear weapons must be legal.
While the President retains constitutional authority to order some military action, Kehler explained that the nuclear decision process "includes assessment, review and consultation between the President and key civilian and military leaders, followed by transmission and implementation of any presidential decision by the forces themselves."
Gen. John Hyten, the commander of US Strategic Command, has shared what would happen if he were ordered to launch a nuclear strike.
"I provide advice to the President," Hyten said in November during a Senate Foreign Relations Committee hearing. "He'll 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.' Guess what he's going to do? He's going to say, 'What would be legal?' And we'll come up with options of a mix of capabilities to respond to whatever the situation is, and that's the way it works. It's not that complicated."