When James B. Steinberg, the deputy secretary of state, sat down in September 2009 with one of China’s most powerful officials, Dai Bingguo, state councilor for foreign affairs, Mr. Dai joked that in a recent visit to North Korea he “did not dare” to be too candid with the ailing and mercurial North Korean leader. But the Chinese official reported that although Kim Jong-il had apparently suffered a stroke and had obviously lost weight, he still had a “sharp mind” and retained his reputation among Chinese officials as “quite a good drinker.” (Mr. Kim apparently assured Mr. Dai during a two-hour conversation in Pyongyang, the capital, that his infirmities had not forced him to give up alcohol.)

But reliable intelligence about Mr. Kim’s drinking habits, it turns out, does not extend to his nuclear program, about which even the Chinese seem to be in the dark.