The core challenge: stopping nuclear fuel production

President Trump’s success or failure in moving toward his stated goal of denuclearizing North Korea may hinge on the fate of a remote, heavily contaminated nuclear site that has been under watch by American intelligence since the early 1980s.

It is called Yongbyon, and it is the centerpiece of North Korean nuclear fuel-making. Declassified C.I.A. documents show that for more than 35 years the United States has been watching for signs that the site’s reactors are operating, as well as tracing what happens to the plutonium — and more recently uranium — that can be turned into bomb fuel there.

If Mr. Trump can get the production of nuclear fuel at Yongbyon stopped, he will have at least “frozen” the North’s program, though it may already have 30 nuclear weapons. That means dismantling the old reactor, neutralizing a new one, and taking apart a uranium enrichment facility that the North showed nine years ago to Siegfried Hecker, the former head of the Los Alamos National Laboratory. (American intelligence officials believe there is at least one other such facility, outside the high walls surrounding Yongbyon.)

Mr. Trump has been told that if he can get the facilities destroyed, he will have made progress no other American president has. If he cannot, the North Koreans will keep producing fuel — and maybe bombs — while talks drag on. — David E. Sanger

Redefining success in the summit

Mr. Trump once vowed to “solve” the problem of North Korea, making clear that he meant eliminating its nuclear arsenal. But he now sounds prepared to accept much less.

As David Sanger and Choe Sang-Hun write, Mr. Trump has moved away from using denuclearization as a measure of success, instead citing the dialogue itself and his relationship with Mr. Kim as measures of progress.