The Senate Intelligence Committee is due to vote on Wednesday on whether to approve Haspel.
After Wednesday's closed-door committee vote, the full Senate will likely consider her confirmation next week.
"The United States must send a message to the world that we hold ourselves to a higher standard than our enemies".
Referring to Haspel's role in overseeing torture and then ordering the shredding of videotapes of torture sessions, Donnelly said, "I believe that she has learned from the past and that the Central Intelligence Agency under her leadership can help our country confront serious global threats and challenges".
Senator Mark Warner said it had been a "difficult decision", but cited Haspel's 33-year career at the CIA and support from its workforce and past intelligence community leaders.
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White House spokeswoman Sarah Sanders on Friday refused to confirm or deny what Sadler had said. He left Washington in December and underwent surgery last month for an infection.
Haspel's comments went beyond her testimony at her confirmation hearing last week, when she repeatedly refused to disavow techniques such as waterboarding as immoral or ineffective. A number of Democrats and two Republicans, Rand Paul and John McCain, have said they'll oppose her confirmation because of her role in supervising the use of the disputed techniques on suspected terrorists in the years after the September 11 attacks. Joe Manchin of West Virginia, Joe Donnelly of IN and Heidi Heitkamp of North Dakota.
McCain, a war hero who was tortured as a prisoner of war in Vietnam, is one of just two Republicans who have announced they will vote against her. John McCain of Arizona is absent.
In her Monday letter, Haspel said that she would refuse "to undertake any proposed activity that is contrary to my moral and ethical values".
He also cited the support for Haspel by former CIA directors under the Obama administration, Leon Panetta and John Brennan, and General Michael Hayden, first appointed director of the National Security Agency by Democratic President Bill Clinton and later CIA director under George W. Bush. At the same time, she appeared to implicate those members who did know about the interrogation program.