President Trump. (Susan Walsh/AP)

Nicholas J. Rasmussen, who stepped down in December after three years as director of the National Counterterrorism Center, has served in senior national security positions under Presidents George W. Bush, Barack Obama and Trump.

Looking back over the past 15 months, it is difficult to imagine any serious observer could have predicted we would have transitioned so swiftly from potential “ fire and fury ” on the Korean Peninsula and talk of “ bloody nose ” strikes to discussions about whether President Trump deserves the Nobel Peace Prize for his work on the North Korea nuclear problem. Suffice to say , anybody betting a dollar on that outcome would have received pretty long odds.

But the fact is the administration finds itself with a genuine opportunity to produce a positive outcome for both U.S. and international security. Taking advantage of that opportunity will require patience and discipline — traits typically not associated with Trump administration foreign policy — and will also require the president to be willing to show increased range and flexibility in how he employs the various tools in his diplomatic toolbox.

Assigning credit for who or what produced this potential foreign-policy success is today both unnecessary and premature. At this early stage, we cannot know what mix of internal and external factors, motivations, pressures and impulses has brought Kim Jong Un to this place. We also cannot know whether his declared willingness to give up his nuclear weapons program will be borne out at the negotiating table.

But having reached this point largely while running counter to conventional wisdom and expert opinion, Trump must now resist the natural impulse to double down on a set of tactics that, from his perspective, has worked brilliantly. Those tactics — bravado and bluster about U.S. military options; disregard for conventional diplomatic approaches and the constraints of coalition diplomacy; a willingness to appear reckless and risk rapid escalation; serial name-calling; and a tendency to personalize the conflict between North Korea and the United States — may be exactly the wrong set of tools for the next phase.

The hard work of negotiating verifiable arrangements to dismantle North Korea’s nuclear weapons program now begins in earnest. Success in that endeavor likely requires a different mix of inputs. First, it will require patience, as these negotiations are destined to be complex and difficult. Treating the upcoming summit as a one-time, is-Kim-serious-about-a-deal-or-not meeting could create a manufactured crisis if diplomacy is viewed as having failed after one encounter between the leaders.

Second, success will require that the president reexamine the sources of U.S. leverage, with Kim having seized the moral high ground internationally with his emergence as a peacemaker. Threats of unilateral military action against Pyongyang could be deemed credible in the context of provocative North Korean missile tests. Are those same threats credible if Kim has suspended the tests and is visibly engaged in reconciliation with Seoul? And if the nuclear talks do fail, Trump will need to have a viable maximum-pressure option to fall back on, tied to even stricter sanctions. That option will be available to him only if South Korea, China and Japan are in lockstep with U.S. strategy.

Third, success will require that the president and his team be willing to listen to and learn from individuals who have significant direct experience in negotiating with North Korea. Even if he views their efforts as having failed, there is much his team can gain from those experiences. Some of those career officials still serve in government, and it would be a tragic mistake not to seek their wisdom and counsel.

As he seeks to turn the objectives proclaimed by Kim and South Korean President Moon Jae-in into concrete progress, Trump must turn to career professionals to answer critical questions and shape his strategy. If presented with the right set of incentives, is Kim truly willing to disarm in a verifiable way? What technical monitoring and verification arrangements will the United States require? How do we ensure Pyongyang will reap the benefits of any agreement only after it takes real steps to dismantle its nuclear capability? To what extent can we count on Beijing, Tokyo and Seoul to align with our strategy, or at least not undermine it?

It will take an unprecedented degree of discipline and self-awareness for the president to realize the recipe that brought us to this point might not be the same as the one that would allow him to get the deal he so clearly wants. It falls to national security adviser John Bolton, Secretary of State Mike Pompeo, Defense Secretary Jim Mattis, and the president’s key intelligence advisers, Director of National Intelligence Daniel Coats and acting CIA director Gina Haspel, to ensure that these questions of strategy and tactics are given a fully informed airing and debate before the president sits down with Kim. All Americans — regardless of whether they support the president — have a stake in his success.