The Church Commission.
The purge of James Jesus Angleton, and more importantly the effective end of the agency's counterintelligence function, which is very much a part of this particular screwup; it's never a popular thing, no one likes being told their informant is a double, but ignoring the possibility is lethally expensive. (See also Aldrich Ames, who's lifestyle should have been caught by counterintelligence as another example of a failure in this area.)
Jimmy Carter's DCI, Stansfield Turner, and e.g. how he riffed 800+ HUMINT operators in just one purge.