Brennan served in the CIA for a quarter-century before leaving government and later joining Obama's initial presidential campaign. In the written answers, he suggested that the CIA's focus on lethal operations has harmed its core mission of gathering intelligence, saying that despite soaring budgets, the turmoil of the Arab Spring showed that the CIA "needs to improve its capabilities and its performance."
He also reiterated his assertion that he lodged private protests with CIA colleagues in the aftermath of the Sept. 11, 2001, attacks over the agency's embrace of brutal interrogation techniques including "waterboarding."
Brennan said he was "aware of the program but did not play a role in its creation." He said he had "significant concerns and personal objections" and "voiced those objections privately with colleagues at the agency."
Former high-ranking CIA officials who worked closely with Brennan said they could not recall him ever raising any objections to the interrogation program.
Brennan, who was once forced to retreat from comments about the absence of civilian casualties in drone strikes, was asked by the committee to provide an estimate, and explain the evidence for it.
Brennan resisted, acknowledging that there have been civilian casualties but saying that they are "exceedingly rare, and much, much rarer than many allege."
Brennan also disclosed on the Senate questionnaire that he had been questioned by the Justice Department in connection with leak cases that center on disclosures about U.S. cyberattacks on Iran and the disruption of an al-Qaida plot in Yemen.
Brennan said his lawyer has been advised that he is "only a witness in both investigations," and not a target.