When the American president tweeted on Tuesday evening that his “Nuclear Button” is “bigger & more powerful” than the North Korean leader’s, and that “my Button works!” unlike the desktop button that Kim Jong Un had just threatened the United States with in a New Year’s speech, Twitter naturally exploded with angst.

People wondered whether they were hallucinating, whether their final moments would involve “reading Twitter hot takes as nukes rain down.” “Folks ... are freaking out about the mental instability of a man who can kill millions without permission from anybody,” one former Obama administration official wrote. Setting aside the technicalities of Donald Trump’s boast (he has a briefcase, not a button), the commander in chief was casually sounding off on social media about war with the world’s deadliest weapons, apparently after watching Fox News. He was daring Kim to prove that his “nuclear button” works by, for example, testing a missile with a live nuclear weapon over the Pacific Ocean—the kind of scenario that the Republican Senator and Trump confidant Lindsey Graham recently told me would dramatically increase the chances of a U.S. attack on North Korea.

But lurking behind the freakout was a profoundly uncomfortable fact: Trump was stating, in the crudest possible form, what U.S. officials have said for decades. Kim Jong Un had argued that his capability to hit the United States with nuclear weapons would dissuade the U.S. from waging war against North Korea. And Donald Trump seemed to be reminding Kim that he best not consider a nuclear strike—since America’s nuclear-weapons arsenal is superior to North Korea’s and America isn’t afraid to use it. This was nuclear deterrence, in 280 Trumpian characters. Stripped of the usual abstraction and euphemism, it was terrifying to behold.

In 1958, the U.S. military strategist Bernard Brodie didn’t taunt the rising nuclear power at the time, Russia, by tweeting “my Button works!” But he did write that deterrence in the Atomic Age operated on a “sliding scale” in which any functional nuclear weapon provided considerable deterrence and the “maximum possible deterrence” required “‘decisive superiority’ over the enemy.” When the Cold War ended, a Defense Department committee didn’t recommend that America’s deterrence policy be “I too have a Nuclear Button.” But it did declare that the “essential sense of fear is the working force of deterrence” and that the United States should convey to adversaries in ambiguous terms that it “may become irrational and vindictive if its vital interests are attacked.” It praised Bill Clinton for informing the North Koreans that if they ever used nuclear weapons, “it would be the end of their country.” Be it John F. Kennedy or Ronald Reagan or Barack Obama, American presidents have spoken passionately not about how “big & powerful” U.S. nuclear weapons are, but about the need, as Kennedy put it, to abolish these weapons of war “before they abolish us.” But every American president since Harry Truman, while engaging in efforts to restrict and scale back nuclear proliferation, “has sought to maintain, in the words of John F. Kennedy, a nuclear-weapons capability ‘second to none,’” as the former arms-control official Robert Joseph has noted. There’s a long, bipartisan tradition of “My nuclear button is bigger and better than yours”—or, at least, as big and as good as yours.

“Any threat to the United States, or its territories … or our allies will be met with a massive military response—a response both effective and overwhelming. … We are not looking to the total annihilation of a country—namely, North Korea. But, as I said, we have many options to do so,” Defense Secretary James Mattis tells us, not on Twitter but before cameras at the White House. “There is no substitute for the prospect of a devastating nuclear response” from America’s nuclear-capable bombers, intercontinental ballistic missiles, and submarine-launched missiles to deter a nuclear first strike by U.S. adversaries, says Air Force General Paul Selva. This nuclear triad, he contends, must be kept up-to-date since “deterrence really is no different in the 21st century than it was in the 20th century or the 19th century or the 1st century B.C.—‘You hurt me, I’m going to hurt you worse. I have the tools to do it, and if you don’t believe me, then step over the line.’” The Pentagon recently created an entire microsite devoted to these themes. In one video on the site, John Hyten, the top U.S. nuclear commander, asserts that “strategic” deterrence “starts with the nuclear capabilities” and that “our nuclear forces have to be ready all the time to provide that initial deterrent capability,” as forbidding images of missiles, submarines, aircraft, and launch switches flash across the screen. If Trump had tweeted “I too have a Strategic Deterrent and our Nuclear forces are always ready to provide that initial Deterrent capability!”—if he had cloaked his warning in conventional presidentialese—he might have sowed less panic on Twitter. But the substance of his message wouldn’t have changed much.

Even Trump’s reference to the mythical nuclear button—to the U.S. president’s largely untrammeled authority to order the use of nuclear weapons—has roots in deterrence theory. As the historian Alex Wellerstein has written, “While nuclear launch officers are not meant to be strictly mechanical (and indeed, the United States has always resisted fully automating the process), if they stopped to question whether their authenticated orders were legitimate, they would put the credibility of U.S. nuclear deterrence at risk.” Trump’s singularly coarse, aggressive, and unpredictable approach to conducting foreign policy—and particularly to countering North Korea’s nuclear program—has moved many Americans to think about the unthinkable and look U.S. nuclear policy squarely in the face. This fall, for instance, a congressional foreign-affairs committee held the first hearing in 41 years on presidential power over nuclear weapons. “Donald Trump can launch nuclear codes just as easily as he can use his Twitter account,” observed Democrat Ed Markey, who has introduced legislation to prevent the president from authorizing the first nuclear strike in a conflict without a congressional declaration of war. “No one human being should ever have that power.”

Beatrice Fihn, a campaigner to eliminate the world’s nuclear weapons, said something similar shortly before accepting last year’s Nobel Peace Prize. “If you’re uncomfortable with nuclear weapons under Donald Trump, you’re probably uncomfortable with nuclear weapons, because it means you recognize that [deterrence] won’t always hold up and things can go wrong,” she told me. “Once you start thinking ‘this person is appropriate for this weapon but not that person,’ then maybe it’s the weapon that’s the problem.”