The Church on time
The last and only time that elected officials looked closely at the abuse of intelligence privileges for political purposes was when the "Church Committee," headed by Senator Frank Church of Idaho, produced its report in 1975. The activities uncovered included not just efforts to assassinate international leaders and destabilise governments around the world, but also another question that has been gathering attention recently: the use of intelligence powers to spy on US citizens. A selection of Church Committee documents is available in PDF form online. It would seem to make for timely reading again.
The director of the CIA at the time when the Church Committee issued its report was one George Bush. The secretary of defence was some guy named Donald Rumsfeld. Frank Church lost his reelection bid in 1980 and passed away in 1984, and neither of the others has been heard from since.