Kim Jong Un never, not once, promised to abandon his nuclear weapons. It was always South Korean diplomats who framed his aspirational comments about denuclearization as a concrete pledge. What Kim wanted was recognition. Kim wanted the United States to accept North Korea as a country, Kim as a ruler, and his nuclear weapons as a fact of life. What he was willing to trade for this recognition was better behavior -- an end to nuclear testing and ICBM flights, plus promises not to export nuclear technologies to other states and a reduction in tension on the Korean Peninsula.

Trump, by contrast, saw something completely different. He believed, egged on by Mike Pompeo who as director of the Central Intelligence Agency briefed Trump regularly on intelligence matters, that his campaign of maximum pressure and nasty tweets would force Kim to disarm. Trump wanted a summit, but that summit was always planned as a triumph -- Trump would arrive in Singapore to collect Kim's weapons.

There were many diplomats who tried to paper over this yawning gap in expectations -- the South Koreans, who framed Kim's statements in the most positive light possible, and Pompeo, a naif in international diplomacy who was suddenly expected to deliver on his flattering comments to Trump about how well the pressure campaign was working.

(Jeffrey Lewis)

But there were others pushing them apart. In the United States, John Bolton, the new national security advisor, undertook a deliberate campaign to misalign Trump's expectations, likely because he opposed negotiations from the beginning and because he wanted to dim Pompeo's rising star.

Bolton incessantly trolled the North Koreans by talking about the Libya model. Bolton knew exactly what he was doing. What world leader would agree to follow Gaddafi to the grave?

Until this week, the North Koreans had largely let the South Koreans do the talking. But then Bolton started yammering on about Libya. It was too much for them to take. We now know the situation began to deteriorate weeks ago. The North Koreans were refusing to return American calls, even standing up a U.S. delegation in Singapore. The North Koreans finally trotted out two senior officials -- Kim Kye Gwan and Choe Son Hui.

It was Choe's comment that was the straw that broke the camel's back. She said that the United States had asked for the summit. That was too much for Trump, whose letter makes clear that he was under the impression the North had asked. He said it was irrelevant, but the prominent clarification said otherwise. In the end, the process had been driven by Trump's ego. But Kim has an ego, too. And it seems Singapore isn't big enough to fit them both.

(Jeffrey Lewis is director of the East Asia Nonproliferation Program at the James Martin Center for Nonproliferation Studies, Middlebury Institute of International Studies at Monterey. He will publish a Japanese translation of his most recent book titled "The 2020 Commission Report of the North Korean Nuclear Attacks Against the United States" in the near future.)