President Donald Trump won’t meet with North Korean leader Kim Jong Un for a historic summit after all — possibly putting Washington and Pyongyang on a path toward war once again.

In a letter to Kim on Thursday, the president explained why he didn’t want to meet with Kim any longer. “Based on the tremendous anger and open hostility displayed in your most recent statement, I feel it is inappropriate, at this time, to have this long-planned meeting.”

Trump is likely referring to a Wednesday statement by North Korean Vice Foreign Minister Choe Son Hui in which she warned that North Korea “can also make the U.S. taste an appalling tragedy it has neither experienced nor even imagined up to now,” according to the state-run Korean Central News Agency.

She also called Vice President Mike Pence a “political dummy” for threatening to attack North Korea and said US actions would determine whether there would be a meeting or whether this would all end in a “nuclear-to-nuclear showdown.”

It’s a stunning turnaround, considering that early last week it seemed like the June 12 summit in Singapore would take place. But suddenly, it all fell apart.

There are two main reasons why. First, National Security Adviser John Bolton angered North Korea on May 14 by suggesting that it follow the so-called “Libya model” to dismantle its nuclear program — a line Pence has continuously propagated.

That’s a no-go for Pyongyang because of what happened to Muammar Qaddafi, Libya’s former dictator. Qaddafi had a nuclear weapons program up until 2003, but he made a deal with George W. Bush’s administration to hand over their nuclear materials and tell the US government where it had acquired the weapons.

Then in 2011, anti-Qaddafi rebels captured and killed him — with American help. Had Qaddafi kept his nuclear weapons, it’s entirely possible the US would not have intervened during the country’s civil war and Qaddafi would not have met such an end. Kim has likely internalized that lesson.

“Kim Jong Un does not want to end up like Qaddafi, overthrown with Western military assistance after giving up his nuclear weapons program,” Kelsey Davenport, a nuclear expert at the Arms Control Association, told me last week.

That leads to the second issue: The US and North Korea couldn’t agree on what to do with Kim’s nuclear program.

Trump wanted Pyongyang to give up all of its nuclear weapons and repeatedly boasted that he expected Kim to do so. But North Korea never said it would end its nuclear program, though it did say it would stop testing missiles and nuclear bombs and destroy a nuclear testing site.

Trump’s demand rankled North Korea.

“If the US is trying to drive us into a corner to force our unilateral nuclear abandonment, we will no longer be interested in such dialogue and cannot but reconsider our proceeding to the DPRK-US summit,” said Kim Kye Gwan, a vice foreign minister for North Korea, on May 16.

And now there is no summit — something experts somewhat expected. “The summit was a rush decision and quickly overtaken by unrealistic expectations,” Davenport told me.

The question now is what happens next?

From a possible summit to a possible war

In an interview, MIT nuclear expert Vipin Narang ranked four potential scenarios, from best to worst, about what could happen if the June 12 summit was called off.

First, both sides may end up deciding to delay the summit because they realize they’re too far apart on the denuclearization issue. That would give Secretary of State Mike Pompeo and lower-level staffers more time to bridge the yawning gaps. And if they come to some sort of understanding, then the leaders can meet to finalize a deal. This, by the way, is how diplomacy usually works.

Second, Washington and Pyongyang delay the summit but make no significant progress toward an agreement because of how far apart they are on ending Kim’s nuclear program. The status quo holds, but relations between the two countries remain better than they were in past decades because they’ve now held direct talks.

Third, “the temperature rises just as quickly as it falls and we go back to 2017,” Narang said.

That means North Korea could return to testing missiles, and the US may increase sanctions. Recall that just last year Trump promised to rain down “fire and fury” on North Korea if it kept threatening the US and its allies. Kim, in response, vowed to “surely and definitely tame the mentally deranged US dotard with fire” for openly talking about destroying North Korea.

And fourth, those words become reality as the United States and North Korea do the unfathomable: They go to war. The Trump administration pursues “denuclearization by force,” Narang said, “using the failed summit as evidence that diplomacy is futile.” But of course, he noted, “that would mean attacking a nuclear weapons power.”

Narang told me he thinks the second scenario — a delayed summit with no diplomatic progress — is the most likely one. Perhaps more importantly, he believes a full-blown war is the least likely, in part because Pyongyang has nuclear weapons, making an invasion very risky because the North could use them on America or regional allies South Korea and Japan.

But let’s be clear: Now that the summit has fallen through, the risks of war — no matter how low the odds — go up.

Why war is by far the worst option

Pompeo echoed Trump when he told the House Foreign Affairs Committee on Wednesday that “a bad deal is not an option. The American people are counting on us to get this right. If the right deal is not on the table, we will respectfully walk away.”

And it looks like the US did just walk away. But the bad news is the two sides are already threatening each other again. On Monday, Vice President Mike Pence said North Korea could end up like Libya — ruthlessly bombed by Western airpower and with its leader forcibly deposed — “if Kim Jong Un doesn’t make a deal.”

That comment shows the specter of war between North Korea and the United States hasn’t gone away. My colleague Yochi Dreazen reported on what a horrific outcome that conflict would be. Here’s just a taste:

The nonpartisan Congressional Research Service estimates that Kim could hammer the South Korean capital with an astonishing 10,000 rockets per minute — and that such a barrage could kill more than 300,000 South Koreans in the opening days of the conflict. That’s all without using a single nuclear, chemical, or biological weapon... Kim would try to level the playing field by using his vast arsenal of chemical weapons, which is believed to be the biggest and most technologically advanced in the world. (Kim is estimated to have between 2,500 and 5,000 metric tons of deadly nerve agents like sarin, which can cause paralysis and, ultimately, death.)

As Dreazen ultimately finds, “A new war on the Korean Peninsula wouldn’t be as bad as you think. It would be much, much worse.” And he notes that you could expect that millions — plural — would die.

War, then, is by far the worst alternate option now that there is no summit. Most experts hope Trump and Kim will stick with a diplomatic approach for as long as possible.

“Leaders in the region and around the world should be leaning on the United States and North Korea to pursue substantive, pragmatic dialogue,” says Bell, now a nuclear expert at the Center for Arms Control and Non-Proliferation. “It’s the only way to solve this crisis.”

The question is whether Trump and Kim continue to believe that — and whether they’re willing to actually sit down together in the future to see if there’s a deal to be had.