Mr McCain, a US Navy veteran who was tortured as a prisoner of war in Vietnam, said Ms Haspel’s failure to deem such practices immoral was “disqualifying”.
"I believe Gina Haspel is a patriot who loves our country and has devoted her professional life to its service and defence,” he said in a statement. “However, Ms. Haspel’s role in overseeing the use of torture by Americans is disturbing. Her refusal to acknowledge torture’s immorality is disqualifying."
Ms Haspel is a 33-year CIA veteran who briefly oversaw an American “black site” prison where at least one detainee was waterboarded in 2002. She also wrote a cable ordering the destruction of nearly 100 videotapes of CIA waterboarding sessions in 2005. The CIA maintains her supervisor was the one to sign and send the cable.
Ms Haspel vowed never to reinstate the CIA’s interrogation programme during her Senate confirmation hearing on Wednesday. But the promise did not satisfy several senators, who wanted her to disavow the programme completely.
In a testy exchange with Senator Kamala Harris, Ms Haspel refused to reply “yes” or “no” when asked if the interrogation techniques – which have been criticised by dozens of human rights groups and several foreign governments – were immoral.
“What I believe sitting here today is that I support the higher moral standard we have decided to hold ourselves to,” Ms Haspel said.
Mr McCain announced his opposition to the nominee in a statement shortly after her hearing. The 81-year-old senator is battling an aggressive form of brain cancer, and has not returned to the Senate since December.
In his statement, Mr McCain said he understood that those who participated in the interrogation programme were trying to protect Americans from harm. But, he added, “the methods we employ to keep our nation safe must be as right and just as the values we aspire to live up to and promote in the world”.
“I believe the Senate should exercise its duty of advice and consent and reject this nomination,” he said.
Ms Haspel’s nomination now proceeds to the Senate for a vote. Her confirmation requires a simple majority vote from the chamber, where Republicans hold a 51-49 majority.
Mr McCain and Senator Rand Paul are the only Republicans to have opposed her nomination publically.
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