At the United Nations General Assembly Sept. 19, President Trump called for preservation of sovereignty and slammed leaders in North Korea, Iran, Cuba and Venezuela. Here are key moments from that speech. (Sarah Parnass/The Washington Post)

 Donald Trump devoted a significant portion of his United Nations General Assembly remarks to North Korea’s nuclear and missile developments. Here are four things he told us (and didn’t).

1) The Trump administration really wants us to know that it does not believe North Korea can be deterred.

In recent weeks, top administration officials have suggested that they are not sure if North Korea is rational or deterrable. The link between these two concepts is important. If a leader is rational, he is capable of acting in his own self-interest. By extension, that leader is therefore deterrable, or responsive to coercive threats that instruct him not to take dangerous actions, or face punishment.

Earlier this month, it was primarily national security adviser H.R. McMaster suggesting that North Korea might not be deterrable, but Trump effectively parroted that view in his U.N. speech. By declaring that “Rocket Man is on a suicide mission,” he indicated his belief that Kim Jong Un was unable to act in his own self-interest and is hellbent on his own destruction.

If, in fact, it was true that Kim is not able to act in his own self-interest and unable to respond to deterrent threats, that would help to build the case for preventive war against North Korea. In that scenario, it might actually make sense to pay the horrendous costs of a military confrontation to eliminate a far worse nuclear threat — if one believed it was inevitable that North Korea would use nuclear weapons against the United States and its allies later.

There is no evidence that this is true of Pyongyang — repeat — no evidence whatsoever. North Korea has long had a stated goal of reunifying the Korean Peninsula, but it has been deterred from large-scale military action since the end of the Korean War in 1953. The fact that Kim and his father and grandfather before him managed to stay in power despite long odds suggests that they are masters of survival, and therefore rational calculators.

McMaster’s argument appears to rest on a false premise: that a brutal, loathsome dictator can’t also be a rational actor. History shows the opposite (take the examples of Joseph Stalin, Mao Zedong). The fact that Trump said Kim “is on a suicide mission” is worrisome. If Trump believes this, it could be part of a justification for preventive war. 

The Fact Checker explains what happened to the once not that distant goal of a nuclear deal with North Korea. (Meg Kelly/The Washington Post)

2) The Trump administration wants us to know it has “military options.” But what does that mean?  

In the days leading up to the General Assembly address, both McMaster and Defense Secretary Jim Mattis reminded us that the United States “has military options” for dealing with North Korea. This isn’t surprising. The United States is the preeminent global military power, so strictly speaking it has military options for dealing with every scenario — including the possibility of war on the Korean Peninsula. But while the “option” technically exists, here’s the problem. It is basically impossible to conceive of any military operation that cripples North Korea’s nuclear program and doesn’t result in gruesome retaliation and a massive loss of Korean, Japanese and American lives. 

And here’s what we don’t know. Is the Trump administration seriously considering a first military strike on North Korea — not a response to a North Korean attack, but a preventive war?

In his August “fire and fury” comments, Trump implied a U.S. first strike in response to North Korean threats. In Tuesday’s speech, he indicated a willingness to strike North Korea, but implied this would come if Pyongyang attacked first. “The United States has great strength and patience but if forced to defend itself or its allies, we will have no choice but to totally destroy North Korea,” he declared. This phrasing is troubling but suggests retaliation, not preventive action, and therefore is actually consistent with past U.S. policy.

The McMaster and Mattis military option “reminders” and Trump’s threats may simply be efforts to signal to North Korea that the United States will retaliate if it or its allies are attacked. But if the White House believes North Korea is irrational and undeterrable, it may also be considering first strikes against Pyongyang. We still don’t know what they are hinting at. 

President Trump's political rhetoric on North Korea has differed from before he declared his candidacy to now. (Taylor Turner/The Washington Post)

3) Trump may be talking to his base — and to China.

 When last I wrote, I speculated that Trump’s “fire and fury” comments may have been an effort to feed a hungry base after a spate of White House firings — and to scare China into doing more to restrain North Korea. Trump may have been speaking to the same audiences in the U.N. speech.

The speech sketched a vision of nationalism-based internationalism — a global “America first” doctrine, so he was surely thinking of his supporters. It is also possible that Trump, McMaster and Mattis have been emphasizing military options and raising questions about deterrability because they hope to scare China into cracking down on North Korea’s economy.

Trump administration officials, however, have been totally inconsistent in their rhetoric. Last month, Mattis and Secretary of State Rex Tillerson guaranteed there would be no regime change in North Korea, and Tillerson has repeatedly disavowed military action. If indeed these threats are intended for China, Beijing may not be able to interpret them because they keep changing. They may just read as sloppy signals.

4) The president’s “Rocket Man” rhetoric is dangerous.

Whether Trump believes that Kim is undeterrable, it is dangerous to say that he does. Here’s why. There is precisely one scenario in which Kim Jong Un might rationally use nuclear weapons first: If he believes the United States intends to topple his regime.

Even if Trump is making threats solely to spur action by China, North Korea is no doubt listening. Trump’s characterization of Kim as being “on a suicide mission” may raise the North Korean leader’s fear that Trump shares McMaster’s view: If Kim is undeterrable, then a U.S. first strike may be logical.

If Trump is bluffing, he is also raising the risk of miscalculation and an accidental or inadvertent clash. If he is serious, he is threatening preventive military action that could start the bloodiest conflict since World War II.

The good news remains, however, that the United States and South Korea have been deterring North Korea for almost 70 years. Let’s hope cooler heads prevail and turn to extending this record of success for decades more.

Mira Rapp-Hooper is a senior research scholar at the Paul Tsai China Center at Yale Law School and an adjunct senior fellow at the Center for a New American Security.