THE RESIGNATION of Notra Trulock, the Department of Energy whistleblower in the Chinese espionage scandal, is the latest in a series of pause-inducing events that make the nuclear spying matter increasingly difficult to evaluate. Mr. Trulock's belief that China stole design information about American warheads and that this material came from the American nuclear labs sparked an important and long-overdue reform effort aimed at tightening security at the labs. After a spree of investigations, it became clear that at least some of Mr. Trulock's concerns have considerable merit: Security at the labs has been weak, and Chinese espionage does appear to have netted design information about American warheads.

Far less clear, however, is how much design information really was compromised and what use has been made of it. There is reason to wonder as well whether Mr. Trulock's confidence that the leak came from Los Alamos was reasonable or whether it led him to narrow his search for the spy and focus too quickly on former Los Alamos scientist Wen Ho Lee. In other words, Mr. Trulock may well have stated the overall problem in terms more dramatic than the evidence clearly supported. And his single-mindedness with respect to Los Alamos and Mr. Lee in particular -- which is alleged by some detractors to have been related to Mr. Lee's ethnicity -- also may have closed off significant investigative leads.

All of this makes it hard to take Mr. Trulock's as the last word in this affair. This is compounded by the fact that so much of the actual evidence remains classified that it is impossible to say with any confidence how to weigh his judgments. That subsequent investigations have not uniformly backed him up on key questions should make people wary of his vision of the extent of Chinese espionage at the labs and the damage it caused. At the same time, his contribution in insisting that lab security and Chinese nuclear spying were a problem requiring immediate attention cannot be dismissed.