Be prepared!

North Korea’s latest threats haven’t yet doomed the summit planned between Donald Trump and Kim Jong Un—but they underscore a vital point. The White House should prepare itself and the American people for failure.

Comments from one of the North’s top nuclear negotiators have exposed a basic contradiction in the adversaries’ approaches to the June 12 meeting in Singapore. The U.S. wants to set a quick timetable for North Korea to dismantle its nuclear-weapons and ballistic-missile programs—what it calls “complete, verifiable and irreversible denuclearization.” Kim says he wants to “denuclearize,” but has a much longer timeframe in mind— one that could last decades, until North Korea no longer feels threatened. In the meantime, he expects trade, investment and aid.

None of this should be shocking: The North has merely clarified its opening position. The U.S. could stand to be a bit clearer as well. North Korea seems to have been provoked by the comments of National Security Adviser John Bolton, who says Kim should ship his entire nuclear arsenal to the U.S., as former Libyan dictator Moammar Ghadafi did, before sanctions are relaxed. Ghadafi’s fate may not recommend this approach to Kim.

The U.S. shouldn’t soften its position—but it needs to speak with one measured voice about what denuclearization means.

The U.S. should also be playing down expectations for the summit. Some American officials seem eager to demonstrate that Trump was right to agree to meet Kim without winning any concrete concessions first (or that the U.S. president already deserves a Nobel Prize). Such talk increases the pressure on Trump to return with something, anything, he can call a win.

The differences may turn out to be unbridgeable, and the U.S. should be ready to walk away. Kim can afford to engage in a failing process: The longer talks drag on, the greater the chances that sanctions enforcement will weaken, particularly along the Chinese border.

If talks fail and those nations aren’t willing to follow Washington’s lead, the U.S. is setting itself up for a bigger failure than a busted summit.