The Washington Post reported Tuesday that the U.S. Defense Intelligence Agency believes North Korea has miniaturized a nuclear warhead for its missiles. According to the report, a DIA document states the intelligence community “assesses North Korea has produced nuclear weapons for ballistic-missile delivery, to include delivery by ICBM-class missiles.”

Another intelligence-community analysis, also from late July, estimates the North could have as many as 60 nuclear weapons.

Both assessments suggest the Kim regime is much closer to deploying nuclear-tipped intercontinental ballistic missiles than most analysts believed, even recently.

Both assessments are controversial, and neither formally represents the consensus view of the U.S. intelligence community.

Soon after publication of the Post story, President Donald Trump reacted. “They will be met with fire and fury and frankly power, the likes of which this world has never seen before,” he said Tuesday afternoon, referring to the North Koreans.

Pyongyang’s response was just as quick. A spokesman for the General Staff of the Korean People’s Army issued a 47-paragraph statement ending with a promise that “the tragic end of the American empire will be hastened.”

The military’s rant followed another threat from the army that it was planning to hit Guam, an American territory and the home to Andersen Air Base, with Hwasong-12 missiles—on Sept. 9.

The North’s Guam announcement had a comical specificity—and some thought Trump’s language sounded as if it too were scripted by North Korean propagandists—but the prospect of miscalculation, and therefore escalation, was real.

Escalation looks like it is on the agenda for at least the next several weeks.

President Trump’s warning was apparently intended to avoid such a dangerous cycle, by reinforcing deterrence. And reinforcing deterrence is critical at this moment as deterrence looks like it could, for the first time in decades, fail.

The United States has generally deterred the Kim family regime since the Korean War armistice in 1953. Deterrence worked especially well when the United States, in the eyes of Pyongyang, appeared powerful.

When the U.S. looked weak, however, the North Koreans struck hard. During the late 1960s, for instance, they grabbed the U.S. Navy’s Pueblo from international waters in 1968 and tortured the crew, killing one. The Norks downed a U.S. Navy EC-121 reconnaissance plane the following year in international airspace—31 killed.

Now, the North Koreans may not be deterrable because they think power has shifted away from America. Their sponsors, the Chinese, look like they are about to take over the 21st century and they themselves may think their nukes make them invulnerable.

The danger for the Trump administration is that when Kim Jong Un feels he is able to nuke any part of the American homeland—probably sometime next year—he will attempt to blackmail Washington in hopes of breaking the U.S. alliance with South Korea. If he can force the subsequent removal of 28,500 American service personnel from the peninsula, Kim may feel he can intimidate South Koreans and ultimately destroy their state.

The overarching goal of the Kim family—and the core of its legitimacy—is the reunification of the Korean nation under its rule, something the United States would have to resist. Therefore, the North Koreans could start a chain of events that leads to conflict and perhaps the world’s first nuclear exchange.

It took the Soviet Union and the United States years to work out a relatively stable relationship in which each knew it could deter the other. Soon, the Trump administration will have to figure out whether it can similarly deter the North Korean regime. That determination will be especially difficult to make because no currently serving American official has ever met the most important figure in that ruling group, Supreme Commander Kim Jong Un.

There are signs that deterrence may not be possible. Kim’s regime periodically goes through periods of instability. The most recent period began in January and lasted, it appears, more than a month.

During that time, the minister of state security, Gen. Kim Won Hong, was demoted; five of his senior subordinates were executed; and Kim Jong Nam, the elder half-brother of Kim Jong Un, was assassinated with a chemical agent in Malaysia. On Feb.12, the chief of North Korea’s strategic-missile forces did not witness the launch of a new missile, a sign of instability at the top of the army.

These incidents suggested the ruling group was especially unstable and that Kim Jong Un’s grip on power was weakening. If the ruling group is in fact unstable, then the United States may not be able to deter it.

No U.S. president can permit an unstable ruling group to possess the means to kill Americans by the tens of millions. The Defense Intelligence Agency believes the North Koreans will soon have such a capability.

If Washington cannot disarm them by peaceful means and they are not thought to be deterrable, then the U.S. will almost certainly use force to take away their fearsome weapons.

The logic of deterrence—in this case, the logic of the lack of deterrence—will require one of the most risky policy moves in history.

This is how great wars start.