Editorial: Trump is right to negotiate with North Korea. But he needs a plan.

If it holds, the agreement on talks will have a short-term benefit because North Korea has agreed to suspend what had been a constant stream of nuclear and missile tests while negotiations continue. Administration officials contend that Pyongyang has been moved by the pressure of sanctions, which Mr. Trump has succeeded in intensifying in the past year. While that may be true, the risk is that the regime will follow its well-established pattern: capture the world’s attention with provocative acts; then agree to negotiations to extract economic and political concessions; then break any commitments it has made.

The challenge for Mr. Trump is avoiding another repeat of that cycle. That means setting an achievable goal: A realistic one might be a long-term extension of the freezing of missile and nuclear tests in exchange for limited U.S. concessions. Unfortunately, by agreeing to a summit, Mr. Trump has already handed over one of the largest potential trade-offs free of charge. Mr. Kim will use the event to portray his murderous regime as a legitimate nuclear power able to parlay with the United States on equal terms. He will no doubt demand a U.S. withdrawal from South Korea and a formal peace treaty in exchange for denuclearization, in the hope that Mr. Trump, unlike every previous U.S. president, will swallow those terms.