The resignation of David Wu brings the number of resignations in this Congress to five. Only one resignation -- that of Jane Harman -- had nothing to do with a sex scandal. But let us take a closer look at those sex scandals.
David Wu (D) - Accused of "inappropriate sexual contact" with a girl who was either 18 or 19 years old.
Chris Lee (R) - Revealed to have been trolling for dates/sex on Craigslist with a fake identity; more reports would reveal, after he resigned, that he was especially interested in transgendered people.
Anthony Weiner (D) - Flirted, using his phone to send shirtless and crotch-bulge-revealing photos, with young girls. One girl -- who did not receive sexually explicit photos, but was contacted -- was in high school.
John Ensign (R) - Had affair with a friend's wife and shuffled money and jobs around to cover it up.
In three cases, the trigger for the resignation was not a revelation of sex. Lee and Weiner were flirting; Wu was doing something else. The commonality between Wu and Weiner is that no scandal can be survived if the words "high school girl" appear in it.