North Korea continues to dominate the Trump administration’s energies on foreign policy, and matters do not appear to be improving anytime soon. Recent events have illustrated that even as the strategic situation worsens with North Korea’s steady march toward an operational nuclear strike capability against the U.S. homeland, the potential for a serious nuclear crisis lies just a few words away.

Last week, the U.N. Security Council unanimously passed resolution 2371 imposing a basket of new sanctions on North Korea after its two tests of the Hwasong-14 (KN20), its first missile capable of reaching the continental United States. North Korea responded by threatening “retaliation thousands of times” over and bluntly declaring to the United States that it should not believe “its land is safe across the ocean,” an obvious reference to its increasing ability to target the American homeland with an intercontinental-range ballistic missile (ICBM). In the four days since the passage of the sanctions, the United States has entered uncharted waters, culminating in a direct threat from President Donald Trump. The president’s words either signified his real intent, committing the United States to taking military action against North Korea — which risks nuclear escalation — or they were mere bluster, which undermines America’s efforts to reassure its East Asian allies of U.S. extended deterrence commitments.

Let’s start with the merely bad news. On August 8, The Washington Post reported that the Defense Intelligence Agency believes North Korea is now capable of fitting a compact nuclear warhead on some of the ballistic missiles it recently tested. The agency now estimates the upper range of North Korea’s nuclear inventory to be 60 nuclear weapons, up from 40 just several months ago. While analysts have spent much of the year enthralled by North Korea’s new suite of missiles, this intelligence assessment should refocus attention on the country’s fissile material stockpiles, which are the chief determinant of its ability to scale its nuclear arsenal. This rapid increase in the upper estimate for the North Korean stockpile is almost certainly driven by growing intelligence confidence that North Korea has designed and is employing composite pits for its bombs. Composite pits use both plutonium-239 and highly enriched uranium-235, enabling a country that may be fissile material-poor to maximize warhead production. With composite pit designs, North Korea will likely be able to field an impressive operational nuclear-armed ICBM arsenal, with enough fissile material left over for its medium- and intermediate-range systems.

Combined with the two successful Hwasong-14 ICBM tests in July, the Defense Intelligence Agency assessment suggests North Korea is fast approaching the point of being able to deliver a nuclear warhead to the continental United States. While some skepticism persists regarding the status of the country’s reentry vehicle technology, Pyongyang is likely one or two more ICBM flight tests from perfecting this last piece of the puzzle. North Korea has also claimed that both ICBM tests were capable of carrying a “large-sized heavy nuclear warhead,” which may suggest a thermonuclear weapon test is around the corner.

As we have written here before, this is all consistent with North Korea’s long-telegraphed aim of establishing its own version of “full spectrum deterrence” — a diverse nuclear arsenal capable of deterring conflict along the full spectrum of conventional and nuclear attacks. To this end, North Korea seeks short-range nuclear systems for first use against U.S. and allied military bases in the region, while the ICBM is meant to deter the United States from using nuclear weapons against it or invading its territory.

That’s all the bad news, and most of this was true before the latest revelations and war of words. But, as always with North Korea, there’s worse news. Shortly after the revelations from the intelligence community, Trump made an off-the-cuff statement at a press briefing that North Korea “best not make any more threats to the U.S. They will be met with fire and fury like the world has never seen.” Leaving aside that Trump’s rhetoric sounded like something out of North Korea’s own state media, such rhetorical escalation is dangerous regardless of how seriously he meant the threat.

Trump’s threat will be pored over in North Korea — as well as in Japan and South Korea — for its intent. Was he threatening nuclear first use against North Korea, or merely a devastating conventional attack to try to prevent the country from achieving that which it already has — an ICBM potentially capable of delivering a nuclear weapon against the United States — or regime change (which Secretary of State Rex Tillerson ruled out just days earlier)? Given all the mixed signaling out of the administration, one can understand why the North Koreans might be preparing for all possible scenarios: at the very least, a massive conventional attack from the world’s most formidable military, backed by a potent nuclear force orders of magnitude stronger than its own. Or, in the worst (albeit extremely unlikely) case, preemptive nuclear use against it.

First, it bears stating that it’s not unusual in itself for U.S. officials to threaten nuclear retaliation against North Korea. In previous administrations, officials have often threatened an “effective and overwhelming” U.S. military response — but only in response to North Korea’s use of nuclear weapons. This point is critical because the United States has never overtly threatened first use against North Korea. Previous statements were meant to reiterate retaliatory intent, in order to reassure Seoul and Tokyo that they will be protected under Washington’s nuclear umbrella. Although American nuclear doctrine has always left open the possibility of nuclear first use, it is extremely rare for officials — let alone the president — to openly threaten or hint at being the first to launch a nuclear attack. On Wednesday, Defense Secretary Jim Mattis attempted to set the record straight on the conditions for retaliation by releasing a statement noting the “unquestionable commitment” of the United States to “defend ourselves from an attack.” North Korea has long known that the condition for facing ostensible nuclear “fire and fury” has been that it uses nuclear weapons first. Trump’s remarks on Tuesday suggested that this reality has changed.

So how has Trump threatened himself into a corner?

First, if Trump is serious and intends to carry out his threat, someone should explain to him the concept of “first strike instability,” which is particularly acute in the case of North Korea. The general notion of mutually assured destruction and the related idea of nuclear stability — that states don’t use strategic nuclear weapons because it would be mutually suicidal to do so — requires a very specific set of conditions to prevail, namely that both states possess secure second strike nuclear forces (no first strike can completely disarm the adversary’s nuclear forces, making retaliation certain) and that they accept those forces’ vulnerability (neither state attempts to overturn the adversary’s second-strike forces by explicitly targeting its arsenal).

If these conditions exist, there is no incentive for a state to use nuclear weapons first in a conflict because it will assuredly suffer unacceptable damage in retaliation. This is why, in theory at least, mutually assured destruction was considered stabilizing, and the key benefit of the so-called nuclear revolution: Crises do not carry the risk of early nuclear escalation from the outset.

However, the stabilizing features of MAD evaporate quickly if one or both states has reason to fear that its arsenal won’t survive a strike — for instance, if its nuclear arsenal or delivery capabilities are small or vulnerable to attack. Similarly, if the states attempt to make themselves less vulnerable by pursuing counterforce capabilities and strategies that might disarm the adversary, the adversary may worry that it will lose all of its nuclear forces in a conflict and be unable to deter nuclear use against it, stripped of its ability to retaliate.

This should sound familiar. North Korea has a small, vulnerable arsenal, and cannot be at all confident it has a second-strike capability (it only has a limited number of ICBMs and transporter erectors, and presumably only a small number of operational warheads compared to the United States; its ICBMs have not been declared operational).

Moreover, North Korea faces a United States with an explicit counterforce doctrine against its small arsenal – meaning Washington openly intends to try to disarm North Korea of its nuclear and missile forces. On Wednesday, Mattis reminded Pyongyang that South Korea and the United States “possess the most precise, rehearsed, and robust defensive and offensive capabilities on Earth” — a less-than-subtle reference to counterforce capabilities. So, one should not expect North Korea to be particularly relaxed if it thinks the United States is coming after it and its nuclear forces. The most significant destabilizing effect is that the concern for survivability incentivizes a state with a small, vulnerable arsenal to consider preemptive use very early in a conflict: Use the nuclear weapons or lose them.

This is first-strike instability: If Kim Jong Un fears the United States and its allies are coming after his nuclear forces, his dominant strategic move is to use his nuclear weapons as quickly as he can, before he loses them. Failing to do so would result in his demise, so his only choice is to go first, go early, and go massively — even though the United States would almost surely deliver the promised “effective and overwhelming” retaliation for first use. Given that Kim’s ICBM arsenal might be gone in the first wave of even conventional attack, he simply cannot afford to go second. He may be left with too little — if anything at all — to penetrate American missile defenses if he waits for the cavalry to reach Pyongyang first.

This is why Trump’s off-the-cuff threats matter so much. Kim may view any efforts to carry out this threat as a possible prelude to regime change or an invasion, leaving him with no choice but to take the president at his word (we wonder how “fire and fury” translates in Korean). After a remark like this — which no doubt reinforces Kim’s fear of American-led disarmament or regime change — a “show of strength” that was actually carrying out this threat, or misperceived to be doing so, could quickly find the United States and its allies facing North Korean nuclear first use.

Put simply: new nuclear states with small arsenals faced with the threat of invasion or regime change can have incredibly itchy trigger fingers. It is important that Trump not rub poison ivy all over those fingers and make them even itchier.

If, however, Trump is blustering and has no intention of carrying out his threat in the face of future North Korean provocations, the bluff also carries significant strategic consequences. For one, it would undermine U.S. extended deterrence assurances and strengthen Kim Jong Un’s desire to “decouple” U.S. formal allies — South Korea and Japan — from the American alliance architecture. This was one of the chief strategic concerns regarding North Korea’s acquisition of an ICBM that we highlighted here last month.

Tokyo and Seoul can reasonably worry whether the United States will be deterred from carrying out this threat because North Korea can now hold the U.S. homeland at risk. Bluffing after such an explicit threat blows an ICBM-sized hole through American efforts at reassuring its allies in the region that it will be there for them when the shells start flying. The implications are severe — and could include Japan and South Korea looking to substitute for U.S. extended nuclear deterrence with their own nuclear weapons capabilities. Debates to these ends are underway in both countries.

There is a reason Washington spends so much on extended nuclear deterrence: The United States has always been allergic to allied nuclear proliferation because it has always wanted Washington, and Washington alone, to be able to control nuclear use and escalation. If three capitals have independent nuclear capabilities, it makes alliance management more difficult as junior allies assert independence from coordinated strategy — a reality demonstrated by France during the Cold War — and also runs real risks of an ally starting a nuclear conflict against U.S. interests. In the latter scenario, the United States would almost certainly be drawn into such a conflict and have to finish it. Therefore, whether Trump means what he said or not, his comments raise the risk of nuclear conflict. Moreover, if Trump’s remark is merely a bluff, it will only embolden North Korea to push the line further on its nuclear weapons and missile programs. Threats are only effective deterrents if there is a credible belief that they will be carried out. This was a uniquely stern and colorful threat. If it is not carried out, it will have exposed a threat made directly by the president of the United States as hollow. North Korea may be tempted to see what exactly constitutes a violation of Trump’s line: verbal threats, scarier verbal threats, missile tests…a nuclear test?

Indeed, hardly three hours after Trump had spoken, the sun had risen in Asia and the August 9 edition of North Korea’s KCNA news agency carried a new and aggressive threat in response to the United States’ recent flight test of a Minuteman-III ICBM, stating that the Korean People’s Army’s Strategic Force was “now carefully examining the operational plan for making an enveloping fire at the areas around Guam with medium-to-long-range strategic ballistic rocket Hwasong-12.” If North Korea were to use nuclear weapons first, Guam would undoubtedly be one of its first intended targets because it hosts a critical American bomber base, Andersen Air Force Base.

On Monday, one day before Trump’s remarks, U.S. Pacific Command flew B1-B bombers over the Korean Peninsula as part of its continuous bomber presence mission in the Pacific. Imagine if such a flight had come on Tuesday after Trump’s remarks. The potential for North Korea to miscalculate based on a perceived U.S. escalation is now far greater. Though the B1-B is now physically incapable of nuclear payload delivery, North Korea believes otherwise, and it may be unable — and would have very little time — to distinguish between “shows of strength” and the opening salvo in a regime change or counterforce effort.

That’s the bottom line: If Trump meant that making even verbal threats against the United States is sufficient to rain “fire and fury” on it, KCNA’s explicit threat against Guam which was written before Trump’s comment, met the condition within hours. Will Trump enforce his threat and use nuclear weapons against North Korea, or initiate efforts at regime change, in retaliation for this provocation? Almost certainly not for this. But in order to test whether Trump’s threat is real or bluster, North Korea may try to push the line to see how far it can go.

All of this makes it even more difficult to set credible lines on North Korea’s behavior and nuclear program in the future. This is not a reality television show — it’s reality. It is tempting to chalk these remarks up to Trump’s shoot-from-the-hip, loose-cannon style and say that everything will be all right because no one should or will take them seriously. But historically, when presidents of the United States speak, nations sit up and take notice. There is no reason to think North Korea will ignore Trump’s words. And now the United States must either carry out the president’s threat and literally risk nuclear war, or admit it was a bluff and risk further emboldening North Korea and eroding the East Asian alliance structure so painstakingly built and reaffirmed for over 60 years.

Words matter, especially when nuclear weapons use is on the line. In a matter of 30 seconds on a Tuesday afternoon, Trump negotiated himself into a disastrous strategic corner.

Ankit Panda (@nktpnd) is a senior editor at The Diplomat and an independent researcher. Vipin Narang (@NarangVipin) is an associate professor of political science at the Massachusetts Institute of Technology.

Image: U.S. Air Force photo by Airman 1st Class Gwendalyn Smith