This faces the U.S. with a problem. U.S. leaders have traditionally been careful with their language, especially when dealing with nuclear powers, and for good reason. If the U.S. cares about its credibility, then it only wants to make threats that it will deliver on. Now, North Korea has effectively called Trump’s bluff. If the U.S. responds as Trump has promised, it will mark a very dangerous escalation. If the U.S. does not respond, then Trump’s credibility — and perhaps U.S. credibility — will be damaged.

Escalation can be a very bad thing

Nuclear weapons are the most devastating kinetic weapons known to man. While fears of a mutual conflagration that would destroy human life on this planet have diminished, even a limited nuclear war could cause millions of human deaths.

Fears of all-out nuclear war dominated the historical relationship between the United States and the Soviet Union. Both sides faced the temptation of brinkmanship — pushing to the very edge of open hostility to extract concessions from the other.

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But brinkmanship is a dangerous game. If you miscalculate your threats or misunderstand the other side’s motivations, you might leave the other side with no choice but to respond aggressively. This might lead to a war of mutually assured destruction that neither side wants but neither side can avoid.

The Cuban missile crisis was a classic example of brinkmanship, in which mutually escalating threats between the United States and the Soviet Union nearly led to war. Had things gone a little differently, the world might have seen a devastating nuclear conflict. The near miss helped provoke serious rethinking on both sides about how they could manage their many conflicts of interest without outright war.

Nuclear weapons led to concerns about credibility and deterrence

After the crisis, U.S. (and eventually U.S.S.R.) strategic thinkers, such as Nobel Prize-winning economist Thomas Schelling, started to radically rethink the politics of conflict. The U.S. and Soviet Union were deeply hostile to each other — but neither wanted a war, and both wanted to avoid the mistakes that might accidentally precipitate one. This is what produced the Cold War, a kind of shadow conflict in which the two countries jockeyed for advantage through proxy conflicts and other means, without ever engaging in direct and open conflict.

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The Cold War happened in the shadow of the hot war involving nuclear weapons that was never actually fought. Each side looked to use implicit or explicit threats to deter the other from doing things it didn’t want it to do, outlining the consequences if their adversaries went ahead.

To be effective, such threats had to be credible. The other side had to believe that the threat would be delivered on, even if it had painful consequences for the threatening party. This meant that leaders — even when they were vociferous in other ways — were extremely careful about even implicit threats of military action against another nuclear power. They feared that if their bluff was called, they would either have to deliver on the threat, risking nuclear conflagration, or face the risk that their adversaries would not believe in their threats in future, greatly damaging their ability to influence their adversaries’ actions.

This is the dilemma that Trump has created

Trump threatened “fire and fury” and “power” against North Korea in a classic example of brinkmanship. Trump is not noted for clarity of language, or for command of the subtleties of international politics, and the threat is rather fuzzily worded. Still, its plain-language meaning would suggest that Trump told North Korea that if it issued any further threats of any sort to the United States, it would suffer dire military consequences. North Korea seems to have decided that Trump’s threat was unbelievable.

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This is unsurprising — there are a number of reasons North Korea might have calculated that Trump was bluffing.

First, a threat of massive military retaliation might seem a disproportionate response to political rhetoric, however threatening. After all, the United States has tolerated — and mostly ignored — bellicose rhetoric from North Korea for decades. North Korea, which has little credibility in international politics, doesn’t have to watch its words as the U.S. does, and has regularly threatened other countries, without delivering on its threats.

Scenes from Trump’s second six months in office share Share View Photos View Photos Next Image Police officers applaud a line by U.S. President Donald Trump (R) as he delivers remarks about his proposed U.S. government effort against the street gang Mara Salvatrucha, or MS-13, to a gathering of federal, state and local law enforcement officials at the Long Island University campus in Brentwood, New York, U.S. July 28, 2017. REUTERS/Jonathan Ernst (Jonathan Ernst/Reuters)

Second, if the United States decides to go to war against North Korea, the country can retaliate. At a minimum, it can use conventional artillery to devastate Seoul and much of the rest of South Korea, which is an important political ally, and it can always threaten to escalate to nuclear warheads.

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Third, North Korea may believe that it can count on the support of China — which is a genuinely formidable power — in a military crisis. Finally, while North Korea has few friends, Trump is a weak U.S. leader who may have difficulty in getting support from key allies.

So what happens now?

The U.S. is now in a difficult situation of Trump’s making. It will be highly costly, and possibly greatly damaging to the United States to deliver on Trump’s threat, even in its minimal form. There is furthermore a significant risk that a spiral of threat and counterthreat might lead to actual nuclear war, which would have devastating consequences.

Yet if Trump, as is more likely, fails to deliver on the threat, then Trump’s credibility, such as it is, will be badly damaged, as might the credibility of the United States in future standoffs. In particular, it will be even harder to influence North Korea’s behavior.