THE multi-faceted relationship between Washington and Beijing was already sufficiently troubled before the weekend report in the New York Times that China developed the technology to miniaturise nuclear bombs, a key step toward fielding a modern nuclear arsenal, by using secrets stolen from a United States government laboratory.
On a variety of fronts - from the World Trade Organisation to anti-missile defences for Taiwan - the optimistic climate apparent during President Bill Clinton's visit to China last summer has turned into something much less sunny. The weekend report adds several twists to the deteriorating pattern, going beyond the alleged stealing of secrets.
The Times cites some officials as saying that the matter was pushed aside for policy reasons because it could have harmed the administration's efforts to develop a strategic partnership with Beijing. According to this account, the White House was informed in the summer of 1997, just before the first summit between Mr Clinton and President Jiang Zemin, and the US government response was marked by delays, inaction and scepticism.
There is a certain irony in the appearance of the story just as Premier Zhu Rongji was delivering his state-of-the-nation address to the National People's Congress. Much of what Mr Zhu said stamped him as a reformer in whom Washington could have faith. Not only did he set out his reformist economic blueprint, but he also sounded a new note towards dissent, warning against the use of 'dictatorial means against the people'.
Espionage between allies - let alone between countries with the history of Sino-US relations - is far from unknown. In a celebrated recent case, an Israeli spy is in prison for life in the US for having passed on military secrets. But the story about China is particularly explosive, evoking memories of Cold War-era spying and the fear of losing the technological advantage in such a key area as nuclear weapons.
If the report is accurate, the administration will find it hard to spin it away to the sidelines. The allegations are simply too grave for that. They provide an additional, and totally unexpected, obstacle for Mr Zhu's visit to the United States next month. However Beijing may react publicly, this is something which the central Government is going to have to take very seriously indeed.