North Korea, which has tested the world’s patience by testing nuclear weapons and ballistic missiles, is now warning the United States that its patience is limited.

The U.S. “should look back on the past one year and cogitate about which will be a correct strategic choice before it is too late,” read a June 5 statement from the North Korea Ministry of Foreign Affairs.

“The U.S. would be well-advised to change its current method of calculation and respond to our request as soon as possible. There is a limit to our patience.”

The U.S. should indeed look back on a year of high-profile summits in Singapore and Hanoi that have enhanced North Korean leader Kim Jong Un’s international stature but not advanced the goal of denuclearization, and conclude that the correct strategy going forward is to reject any further meetings between Kim and President Donald Trump unless and until there is substantive and verifiable progress on denuclearization.

That doesn’t mean that the two sides shouldn’t talk. After all, Trump’s high-stakes gamble of meeting Kim to try to break through decades of enmity was preferable to the escalating bellicosity between the two volatile leaders. “To jaw-jaw is always better than to war-war,” goes the apocryphal quote attributed to Winston Churchill, reflecting the preference of diplomacy over armed conflict. It is in fact better to be talking with North Korea.

But Trump seems focused on summit optics over substance. “I think they would like to make a deal and we would like to make a deal,” Trump said of North Korea while in Ireland last week, adding that he looks forward to meeting Kim again “at the appropriate time.”

The appropriate time is to seal a deal that has been already worked through by both the U.S. and North Korea, not in another high-profile, low-productivity summit in which Kim seeks to seal his international standing.

“The president had a good point in saying that we had tried working from the ground up, having negotiated with a lot of mid-level and even high-level negotiators trying to find common ground, and that hadn’t worked,” Ray Burghardt, a career State Department diplomat who is now president of the Pacific Century Institute, told an editorial writer. “In a country like North Korea where one person really has the power, the idea of having a leaders’ meeting and doing it sort of in reverse of the normal process, having it be a top-down process was worth a try. But I think that that approach can’t make progress any further on its own.”

So envoys like Steven Biegun, U.S. special representative to North Korea, and his Pyongyang counterpart (whoever that may be, given the inconsistent reports that some of Kim’s close associates have been diminished, or imprisoned, or even executed) need to revert to a traditional diplomatic approach to achieve the objective of North Korea relinquishing its nuclear arsenal and to stop developing missiles that can continue to menace neighboring nations, let alone eventually the United States.

This approach will likely take patience, given Kim’s expectation that he can negotiate sanctions relief while still keeping his arsenal — an outcome that must be avoided.