By Daniel Henninger

On July 28 this year, North Korea’s Kim Jong Un tested an intercontinental ballistic missile. Analysts said its potential flight path on an optimum trajectory could travel some 6,400 miles. We can’t help but notice that most of the commentators who are dumping condescension on President Trump for threatening to “totally destroy North Korea” live in New York or Washington rather than Seattle or San Francisco. Or Seoul or Tokyo or anywhere people live who no longer see Kim’s 250-kiloton bomb—about 17 times as big as what hit Hiroshima in 1945—as an intellectual or journalistic abstraction.

Mr. Trump violated foreign-policy sensibilities on the Eastern Seaboard by saying out loud what has been an implicit reality of U.S. strategic policy since the dawn of the nuclear age: We reserve the right to use nuclear weapons to pre-empt a first strike from an adversary, and that includes an enemy’s nuclear, chemical or biological weapons. The reason resided in one simple Cold-War word: deterrence.

Toward the end of the Obama presidency, concerns emerged that Mr. Obama would adopt the “no first use” doctrine on nuclear weapons long favored by progressive arms-control activists. He did not. Also worth keeping in mind amid the outcry that Mr. Trump’s speech violated some sort of international gentlemen’s agreement is that NATO has refused for 70 years to adopt no first use.

Until recently, no American president needed to make such threats in public. An assumption of the Cold War was that the Soviet Union’s leadership ultimately was rational, and so we negotiated nuclear agreements with them. Some similar baseline of assumed rationality attached to dealing with each subsequent nuclear power, such as China, India and even Pakistan.

Pakistan and India—estimated to have more than 100 nuclear warheads each—rattled the world’s nerves as recently as 2002, when the two countries massed armies along their 2,000-mile border after a terrorist attack on the Indian Parliament.

Whether Iran’s revolutionary and messianic religious leadership is “rational” in the Cold War meaning lies at the heart of the disagreement over the Obama nuclear deal with Tehran. The Iranians understood this requirement, and so they put forth as their negotiator Foreign Minister Javad Zarif, a “rational man” from Hollywood central casting, unlike the evil-eye mullahs who actually decide Iranian nuclear strategy, which looks a lot like North Korea’s nuclear strategy. Yet another of Mr. Trump’s violations of Eastern Seaboard sensibilities is to suggest the Iranians are less trustworthy on nukes than, say, Mikhail Gorbachev.

Since 1993, the U.S. has pursued the standard model of rational-man arms control negotiations with North Korea. This false, 25-year-long presumption now has brought us to within perhaps one year of Kim being able to attach a miniaturized nuclear bomb to the cone of an ICBM.

The day that happens, the world will have crossed a Rubicon into a nuclear reality incomparably more dangerous than anything in the previous seven decades. On Tuesday, a U.S. president spoke truth to nuclear power. Eastern punditry will never recover from the way Mr. Trump said it, but the rest of the rational world will adapt.

Adaptation of some sort is needed as well to Mr. Trump’s thoughts on sovereignty, mentioned more than 20 times in the speech. I haven’t anything enlightening to add on this subject because I have no fully graspable idea what he is talking about, and I’m not sure Mr. Trump does either.

The idea of protecting a country’s national security and economic interests is easy enough to understand, for instance when renegotiating a trade agreement between the U.S. and Mexico. Mr. Trump, however, seems to be talking about something more transcendent.

Sovereignty as a mystical force in the lives of nations is an idea brought into the Trump presidency by Steve Bannon and articulated in the U.N. speech and elsewhere by Mr. Trump’s chief speechwriter and Bannon ally, Stephen Miller.

Nationalism and what it means for increasingly volatile populations is a good subject just now, but I don’t think Messrs. Bannon and Miller, for all the time they’ve spent talking about sovereignty, have put across the idea in any feasible operational sense for U.S. policy makers. In practice, that makes it largely irrelevant.

My own tastes in Trumpian philosophizing run more toward statements like this at the U.N.: “Major portions of the world are in conflict, and some, in fact, are going to hell.”

Again, the pundits gagged, presumably nostalgic for the prudent, considered cadences of Barack Obama, whose foreign policies left much of the world, um, going to hell. Aleppo’s bombardment into rubble comes to mind.

Hearing Mr. Obama describe more of the same will cost you $400,000 now. President Trump gets to talk for free about Kim Jong Un’s march toward a nuclear Armageddon. Between these two, I’ll take the free version.