The remark came out seemingly inadvertently when Hersh was asked by the moderator of a public discussion of "America's Constitutional Crisis" whether abuses of executive power, like those which occurred under Richard Nixon, continue to this day.
Hersh replied, "After 9/11, I haven’t written about this yet, but the Central Intelligence Agency was very deeply involved in domestic activities against people they thought to be enemies of the state. Without any legal authority for it. They haven’t been called on it yet."
Hersh then went on to describe a second area of extra-legal operations: the Joint Special Operations Command. "It is a special wing of our special operations community that is set up independently," he explained. "They do not report to anybody, except in the Bush-Cheney days, they reported directly to the Cheney office. ... Congress has no oversight of it."
http://rawstory.com/news/2008/Hersh_US_has_been_running_executive_0311.html