With North Korea, there are two unique complications: It already has an arsenal of nuclear weapons and missiles, including an ICBM that can reach the United States, and the locations of many its nuclear sites are unknown, making verification hard if not impossible.

And since Mr. Trump has denounced the Iran deal, with its uniquely intrusive inspections and strict requirements for significantly reducing nuclear fuel and other nuclear-related components, as the “worst ever,” he has set quite a high bar for an accord with North Korea. In fact, he says he is insisting on “complete, verifiable, irreversible denuclearization,” presumably meaning eliminating all of North Korea’s atomic weapons and production facilities. That outcome would be an extraordinary achievement.

But Mr. Trump has been known to underdeliver on his grander promises, and no nation with a nuclear program this advanced has ever disarmed so completely. So what would a more plausible yet still positive deal look like?

SCOPE: In the Iran deal, Tehran agreed to strict controls on its nuclear program in exchange for economic benefits — sanctions relief. Mr. Trump could seek a broader deal with North Korea by offering wider benefits, not just sanctions relief but also security guarantees and full diplomatic relations. This would allow the administration to pursue curbs on North Korea’s missiles, chemical and biological weapons and technology exports, too. The president has said of Kim Jong-un, “I will guarantee his safety.” That is a ridiculous commitment no president could keep, or want to, since it would have the United States protecting one of the world’s worst human rights abusers. Instead, the administration could promise not to try to overthrow Mr. Kim and could reiterate the pledge the United States made in the 1994 Agreed Framework, to work toward peace on the Korean Peninsula. In exchange, North Korea would curb those other weapons and perhaps resolve the fate of South Korean and Japanese citizens North Korea has abducted. A peace treaty to resolve the Korean War 65 years after an armistice was signed could be considered, if it wouldn’t bog down the nuclear negotiations.

SHORT-TERM GOALS: Mr. Trump thinks he can snap his fingers and get North Korea to eliminate all its nuclear weapons and facilities. Secretary of State Mike Pompeo says to expect “major disarmament” by the end of the president’s first term. Some experts have estimated it could take up to 15 years to fully denuclearize. Many say it’s unrealistic to expect it all. No matter how likely or how drawn out such a grand goal would be, some steps can be taken quickly. As a start, the two sides should agree on a framework for sustained, high-level negotiations, including a definition of denuclearization using the 1992 South-North Joint Declaration as a model. In that agreement the two Koreas committed to limiting nuclear energy for peaceful purposes and not to test, manufacture, receive, store, deploy or use nuclear weapons or nuclear reprocessing and uranium enrichment facilities. North Korea should make its temporary freeze on nuclear and missile testing permanent and allow international inspectors to verify the destruction of the test sites the government claims to have blown up. It could even sign the Comprehensive Test Ban Treaty. Fissile material production should also be frozen. Even if the process ended there, Mr. Trump would achieve something constructive.