The ‘Nuclear Button’ Explained: For Starters, There’s No Button

President Trump and Kim Jong-un, the leader of North Korea, traded threats last year about the size, location and potency of their “nuclear buttons.”

The image of a leader with a finger on a button — a trigger capable of launching a world-ending strike — has for decades symbolized the speed with which a nuclear weapon could be launched, and the unchecked power of the person doing the pushing.

There is only one problem: There is no button.

William Safire, the former New York Times columnist and presidential speechwriter, tracked the origin of the phrase “finger on the button” to panic buttons found in World War II-era bombers. A pilot could ring a bell to signal that other crew members should jump from the plane because it had been damaged extensively. But the buttons were often triggered prematurely or unnecessarily by jittery pilots.

The expression is commonly used to mean “ready to launch an atomic war,” but the writer added in “Safire’s Political Dictionary” that it is also a “scare phrase used in attacking candidates” during presidential elections.

President Lyndon B. Johnson told Barry M. Goldwater, his Republican opponent in 1964, that a leader must “do anything that is honorable to avoid pulling that trigger, mashing that button that will blow up the world.”

Richard M. Nixon told advisers during the Vietnam War that he wanted the North Vietnamese to believe he was an unpredictable “madman” who could not be restrained “when he’s angry, and he has his hand on the nuclear button.”

During the 2016 presidential election, Hillary Clinton said of her opponent, “Trump shouldn’t have his finger on the button, or his hands on our economy.”

Each nuclear-capable country has its own system for launching a strike, but most rely on the head of government first confirming his or her identity and then authorizing an attack.

Despite Mr. Trump’s tweet that he has a “much bigger & more powerful” button than Mr. Kim, the fact is, there is no button.

There is, however, a football. Except the football is actually a briefcase.

The 45-pound briefcase, known as the nuclear football, accompanies the president wherever he goes. It is carried at all times by one of five military aides, representing each branch of the United States armed forces.

Inside the case is an instructional guide to carrying out a strike, including a list of locations that can be targeted by the more than 1,000 nuclear weapons that make up the American arsenal. The case also includes a radio transceiver and code authenticators.

To authorize the attack, the president must first verify his identity by providing a code he is supposed to carry on him at all times. The code, often described as a card, is nicknamed “the biscuit.”

In his 2010 autobiography, Gen. Henry H. Shelton, chairman of the Joint Chiefs of Staff during the final years of Bill Clinton’s presidency, wrote that Mr. Clinton had lost the biscuit for several months without informing anyone.

“That’s a big deal,” General Shelton wrote, “a gargantuan deal.”

The president does not need approval from anyone else, including Congress or the military, to authorize a strike — a decision that might have to be made at a moment’s notice.

Nevertheless, some politicians have called for more layers of approval.

“The longer I’m in the Senate, the more I fear for a major error that somebody makes,” Senator Dianne Feinstein, Democrat of California, said in 2016. “One man, the president, is responsible. He makes an error and, who knows, it’s Armageddon.”

Written by By Russell Goldman