The test firing of what appear to be two North Korean ballistic missiles highlights the flaws of Donald Trump’s style-over-substance approach to nuclear diplomacy with North Korea. The failure of the Trump administration to get Kim Jong Un to agree to anything more substantial than broad-brush statements about denuclearization is becoming a greater liability. Washington should take care not to overreact to this latest missile test, but letting Kim off the hook entirely would also be very unwise.

Trump’s diplomatic engagement with North Korea has emphasized high-profile meetings with Kim that have been heavy on symbolism but light on substance. Working-level discussions did take place between the June 2018 summit in Singapore and the February 2019 summit in Hanoi but stopped after the latter ended in failure. Trump and Kim apparently agreed to restart working-level talks when they met for a “handshake summit” last month, but this diplomatic thaw could now be in jeopardy.

While Kim has, at various times, promised to dismantle his nuclear testing facility and a space rocket launch site, and freeze intercontinental ballistic missile testing, none of these pledges have been formalized through a joint statement or other diplomatic agreement. Trump made a similar, vaguely defined promise that the United States would stop conducting certain military drills with South Korea.

Kim has tried to use the lack of a formal agreement to his advantage by being highly critical of U.S. actions and flexible with his own actions. North Korea has loudly condemned U.S.-South Korean military exercises as violating the spirit of Trump’s verbal commitments to cancel the exercises, even though the drills have been reduced in size and scope. Meanwhile, Kim can say that he is upholding his promise of no ICBM testing even as he tests other ballistic missiles that can threaten U.S. and South Korean military forces on the peninsula.

Trump’s inability to secure an official version of Kim’s promises means that Kim can easily force Trump into a dilemma, as he did with the recent missile test. Reacting too strongly to the tests risks collapsing diplomacy entirely, but a nonreaction could embolden Kim to flirt with breaking more promises in the future. Both leaders could quickly begin pointing fingers at one another for violating the spirit of their agreement at the Singapore summit because the letter of that agreement is so open ended.

This dynamic is likely to continue if Trump and his negotiating team stay stuck on style over substance. This is not to say that the summitry has been a total failure. Leader-to-leader diplomacy is especially important when dealing with a state like North Korea, where so much political power is concentrated in one person. However, recent events show the problems that occur when diplomacy fails to produce substantive agreements. It becomes very easy for expectations about progress to be out of sync with reality, which can cause summits to unravel without agreements and encourage the parties to push the envelope in destabilizing ways.

Trump and other senior officials shouldn’t be afraid to express their concern with the missile test, and the upcoming U.S.-South Korea exercise should proceed as planned. At the same time, the Trump administration should make it clear that it wants to negotiate with North Korea and is prepared to discuss security guarantees, including adjustments to military exercises. The goal of this approach would be to show Kim that there is a way for him to get what he wants, but it will only happen via diplomacy and not provocations.

Kim probably won’t like such a response, but he would face costs for rejecting such an offer. An escalation such as an ICBM launch or nuclear test would risk killing negotiations with the United States entirely. Such actions would also strain relations with China and Russia, who have been willing to support Kim’s diplomatic efforts but supported tougher United Nations sanctions when Kim was stoking tensions in 2017. Beijing and Moscow could keep the North’s economy afloat by loosening sanctions enforcement, but this wouldn’t allow Kim to make much progress on his domestic priority to improve the North’s economy.

Diplomacy with North Korea is messy and it wouldn’t be surprising for many people in the United States to start questioning the point of negotiating in the wake of the North’s latest provocation. But while Trump’s diplomatic approach has significant flaws and leaves much to be desired, there is still value in trying to manage the North Korean problem through diplomacy. This latest setback should cause the administration to adjust, but not abandon, its approach.