White House has confirmed that CIA Director Mike Pompeo met with Democratic People's Republic of Korea's leader Kim Jong-un to discuss with him the planned summit with US President Donald Trump. Since Pompeo is Trump's trusted pick to head the State Department, the meeting is an assuring sign that both parties are serious about making the summit happen.

And if the summit does take place, goes well, and maybe even proves fruitful, that would be an encouraging first step toward a scenario in which all stakeholders would be winners. And one in which denuclearization of the Korean Peninsula turns from rhetoric to specific, verifiable, and irreversible moves.

Republic of Korea President Moon Jae-in has demonstrated a strong personal interest in a thaw in inter-Korean relations, and this has been matched by Kim. Thus next week's planned meeting will likely go ahead smoothly, and culminate in them expressing a shared interest in officially ending hostilities. A successful Moon-Kim summit will certainly make a Trump-Kim one more probable.

But, promising as things look, the US president was correct in his assessment that the productive negotiations he wants are possible, not guaranteed. There is the possibility of his history-making summit with Kim being aborted or failing to produce the concrete outcomes he seems to expect. So Trump may want to think twice about what would qualify the summit being a success. Kick-starting a process of constructive engagement and preserving the positive momentum that has been attained may be more realistic, and is certainly desirable.

It is perfectly understandable for Washington to want tangible outcomes. Every party except Pyongyang wishes to have the nuclear threat removed overnight. But complete, verifiable and irreversible denuclearization will not happen unless Pyongyang feels confident it is safe without nuclear weapons.

The "comprehensive resolution of multiple concerns" that Japanese Prime Minister Shinzo Abe spoke of after talking with Trump, while pleasant to the ear, seems unrealistic. It is more reasonable as a goal, not a precondition. For the historic breakthrough he wants, it may be more advisable to be patient, and persistent throughout.

At least Pompeo appears to be keeping his feet on the ground, having told his Senate confirmation hearing that no one was under any illusion that a comprehensive deal could be reached at the summit.

Let's hope Trump is on the same wavelength.