Such issues would typically be handled by a well-established diplomatic process of lower-level negotiations that usually takes months, if not years, before a meeting between the leaders of two nations. But Mr. Trump short-circuited that process in March, when he abruptly accepted an invitation to meet with Mr. Kim.

Now, after just as abruptly canceling the summit meeting, Mr. Trump has — wittingly or not — set in motion a more normal set of discussions to lay the groundwork for an agreement about North Korea’s nuclear weapons program ahead of a decision on whether to hold a meeting between the two leaders after all.

The timeline is still extraordinarily condensed. Mr. Trump’s repeatedly stated desire to keep June 12 as a possible date for a summit meeting means that officials on both sides are rushing to see if the necessary preparations can be completed in a matter of days. Veteran negotiators said it remained unclear whether the two sides could complete enough work to make a meeting possible.