Hmm, maybe this is why John Kerry didn't want to badmouth him:

Ahmed Wali Karzai, the brother of the Afghan president and a suspected player in the country’s booming illegal opium trade, gets regular payments from the Central Intelligence Agency, and has for much of the past eight years, according to current and former American officials.

You have to wonder what other unsavory things the CIA is up to in Afghanistan. Which may also be a reason why Barack Obama isn't too keen on digging deep into Bush-era agency practices.

P.S. A disturbing addendum from Andrew Exum, who consulted on the McChrystal report:

I can, however, say that numerous military officials in southern Afghanistan with whom I have spoken identify AWK and his activities as the biggest problem they face -- bigger than the lack of government services or even the Taliban. And so if AWK is "the agency's guy", that leads to a huge point of friction between NATO/ISAF and the CIA.