The surge in Iraq is not the reason for the decrease in violence. Instead the reason is "highly classified techniques". This is what Bob Woodward claimed in an interview with Bill Maher. Woodward refused to specify what he meant with the term "highly classified techniques".
The interview took place on Friday the 3rd of October, 2008, (i.e. on the same day the U.S. House of Representatives voted for the financial rescue package).
Woodward has recently published a new book about the Bush administration "The War Within".
Below there is a video clip of the interview from YouTube.
