The French were almost unanimously incredulous when Bill Clinton was being interrogated over his affair with Monica Lewinsky in 1998. I remember trying to explain to a Parisian taxi driver the US president was being pursued not for sexual immorality but for abusing power and lying under oath. Mr Clinton should not be impeached, I said, but, still, “he has acted like a ... a ... what is the word I’m looking for in French?”.

“Un homme?” the cab driver suggested helpfully.

At first glance, the collapse of US prosecutors’ rape case against Dominique Strauss-Kahn, former International Monetary Fund head and French presidential contender, teaches a similar lesson: America’s legalistic doctrines of sexual morality have been held up to the more cynical but realistic French ones and found wanting. This week Cyrus Vance Jr, the New York district attorney, successfully petitioned to drop the charges he brought against Mr Strauss-Kahn in May. Mr Vance cited the inability of the accuser, his chief witness, to tell a straight story about almost anything. But if America’s system of regulating sexual morality has undergone another embarrassing moment, it will be France’s system that has to change.