Brennan was previously considered for the top CIA position by Obama at the beginning of the his presidency in 2009, but that consideration was withdrawn after voices of opposition raised substantial concern about Brennan's involvement with the CIA's torture program which flourished during the presidency of George W. Bush.
Among those concerned were military psychologists and civilian opponents of the torture program who penned an open letter at the time calling on the newly-elected Obama to reject Brennan from consideration. They wrote:
Mr. Brennan served as a high official in George Tenet's CIA and supported Tenet's policies, including "enhanced interrogations" as well as "renditions" to torturing countries. According to his own statements, Mr. Brennan was a supporter of the "dark side" policies, wishing only to have some legal justification supplied in order to protect CIA operatives. [...]
The use of these tactics goes against the moral fiber of our country and is never justified. This is true whether these "enhanced interrogation" techniques are used directly by U.S. forces, as in the CIA's "black sites," or by other countries acting as our surrogates, as in the "renditions" program where individuals are taken to countries practicing torture, resulting in suffering inflicted by that country's forces. [...]