So why, as Biegun himself emphasized during congressional testimony, is North Korea barely engaging in nuclear talks with the United States at the moment, even as the 2020 election approaches with no guarantee Trump will win again? Why is Kim standing by as the Trump Window potentially closes—and actually hastening the closure by giving the U.S. a year-end deadline to adopt a more flexible negotiating position or put at risk nearly two years of diplomacy between the countries?

In recent weeks, in fact, the North Koreans have thrown all sorts of wrenches into the (albeit already gummed-up) diplomatic works, even as Trump has dangled another leader-level summit before Kim and as his administration has made other conciliatory gestures, such as postponing military exercises with South Korea.

North Korean negotiators walked away in a huff from a meeting last month in Sweden with Biegun and his team without seriously discussing denuclearization or consenting to follow-up talks. In a remarkable flurry of statements for a government that typically tightly controls its communications, North Korean officials rejected the idea of another meeting with the American president (something the Kim regime coveted only a couple of years ago) and ruled out further denuclearization talks until the United States ends its “hostile policy” toward their country, including U.S.–South Korea military drills and international economic sanctions.

Read: Trump is running out of time to denuclearize North Korea

The Kim regime “now considers summits without payment for cooperation as empty diplomacy that merely helps ... Trump raise domestic political support,” Leif-Eric Easley, a Korea expert at Ewha Womans University, in Seoul, told me. It’s ironically the mirror-image argument to what Trump’s critics contended when he became the first American president to meet with North Korea’s dictator: that it would grant Kim valuable legitimacy while leaving the United States with nothing of substance to show for it.

Apparently emboldened, this week alone Kim has twice spurned South Korea by declining an invitation to attend a regional conference and by violating a military agreement with its neighbor, making it harder for the South Korean government to do what it has done repeatedly over the past two years: act as a catalyst for diplomacy between the U.S. and North Korea. Kim has also conducted a series of tests of nuclear-capable ballistic missiles since the spring. The not-so-subtle subtext of these provocations is that if the Trump administration doesn’t change its policies to his satisfaction by the new year, Kim could resume the tests of nuclear bombs and long-range missiles that brought the United States and North Korea to the brink of war in 2017.

With six weeks to go until the end of 2019, Biegun told lawmakers that Kim has not yet empowered his negotiators to discuss the country’s nuclear-weapons program with their American counterparts, nor agreed in writing on a suspension of nuclear and missile tests, a definition of denuclearization, or how North Korea would undertake such a process. Instead, he acknowledged that North Korea has continued advancing its nuclear arsenal by, for instance, producing more fissile material. When asked by Senator Cory Gardner whether he believed the United States is closer today to the denuclearization of North Korea than it was after the first Trump-Kim summit, in Singapore 17 months ago, Biegun sighed heavily. “I do,” he said gingerly, but “in all candor there is no meaningful or verifiable evidence that North Korea has yet made the choice to denuclearize.”