To the surprise of everyone — perhaps including both of them — President Donald Trump and North Korean President Kim Jong Un are heading toward a summit meeting. Prospects for "denuclearization" of North Korea appeared to be slipping from view just a few short months ago as Kim pushed ahead with nuclear and long-range ballistic missile tests. The North Korean leader has at least rhetorically put that policy goal back in play, and on Saturday announced that he would stop nuclear tests and launches of intercontinental ballistic missiles. But the emerging narrative of what Washington should expect and demand is now running dangerously ahead of reality and risks dooming any chance for a diplomatic solution to the North Korean crisis.

Trump's agreement to meet North Korea's president was a "win" for Kim, one achieved without any real concessions — Kim's commitment to denuclearization is vague and arguably an empty gesture, but he and his regime will receive a valuable stamp of legitimacy from a high-profile meeting with Trump. That said, as 2017 was concluding, Washington and Pyongyang were on a path toward a devastating war in Asia. The Trump-Kim summit, along with renewed North-South diplomacy, has at least given pause to war. More could and should have been done to support this bold — and risky — summit move in advance, but at a time when hundreds of thousands of lives were hanging in the balance, it was a risk worth taking.

Yet the pressure is already on Trump not to make any further concessions in the absence of concessions from the North. Some have argued that there must be further clarification of what Kim Jong Un means by "denuclearization" to even go ahead with the summit. Yet defining this one word in concept and practice is likely to require months and perhaps years of negotiations, just as the definition of agreed U.S.-Soviet commitments in the Reagan era (e.g., the "zero-zero" proposals to eliminate intermediate-range nuclear missiles in Europe, "50 percent cuts" in strategic nuclear arms) took two presidential terms to hammer out in treaty text.

Given how truly unprecedented the Trump-Kim meeting is, the lack of experience between leaders and the personalities involved, any outcome beyond an agreement to continue a process of dialogue and negotiations beyond the summit may be a bridge too far. This is not to argue against the Trump administration developing a strategy for the summit and beyond — indeed, Kim, who has played his hand extremely well, may be ahead of us here; it is to point out that if benchmarks for a successful summit are set and not met, this may be the last meeting, the end rather than the beginning of a process and an acceleration toward war.

Objectives and provisions — possibly including legally binding text — will be needed in the context of denuclearization. Yet every veteran of international negotiations will attest that not every provision proposed at the outset is required for an agreement that is in our national interest. It is always the provisions proposed and not agreed to that are "Exhibit A" in critics' appraisals. In 1993, President Bill Clinton signed a Presidential Decision Directive mandating our ingoing negotiating position on a Comprehensive Nuclear Test Ban Treaty, including a treaty of limited duration and permitting extremely low-yield testing. Over three years of negotiations, those two positions changed — to the benefit of the United States. But during the Senate debate on ratification, treaty opponents were quick to charge that the administration had "tried and failed."

Pushing now for clarity on denuclearization, benchmarks for a successful summit and expectations for any agreement — all three of these dynamics are now in play inside the Trump administration. The president himself has shown a disturbing propensity for laying down markers that cannot be met; in the case of North Korea diplomacy, he may box himself in now with markers he may regret later.

We can always hope for more and more faster, but the reality of where we are today with North Korea is simply this: A new process of dialogue and negotiation, which had been delayed too long by too many administrations, will take time. It will be fluid and unpredictable. We will learn more as negotiations unfold that will inform our judgments about what can and cannot be achieved. More likely than not, there will be agreements in stages — and in each case, more than one way to achieve our vital interests, including diluting North Korea's threat to the U.S., South Korea and Japan and avoiding a devastating war on the Korean Peninsula. Beyond that, for now, the less written in stone about what the U.S. "must" have, and the more realistic our ambitions, the better.

Steve Andreasen, the director for defense policy and arms control on the National Security Council staff from 1993 to 2001, is a national security consultant who teaches at the University of Minnesota's Humphrey School of Public Affairs.