(CNN) Several key Republican senators say Gina Haspel will have to answer for her role in the CIA's interrogation and detention program before she can be confirmed as the next CIA director, a signal that she faces a bruising and potentially difficult confirmation battle ahead.

President Donald Trump's pick to succeed Mike Pompeo at Langley is a 30-year CIA veteran who is currently deputy CIA director. She ran a CIA "black site" prison in Thailand in 2002, and she later played a role in the CIA's destruction of tapes of the interrogation sessions of terrorism detainees.

Democrats are already gearing up in opposition and plan to make Haspel's role in the George W. Bush-era CIA interrogation program a key part of her confirmation, while human rights groups are pressing for the CIA to declassify her records in the program.

But the only way Haspel's nomination is in jeopardy is if she loses the support of Republicans, who hold a slim 51-49 seat majority in the Senate.

Their support is not yet assured.

"The torture of detainees in US custody during the last decade was one of the darkest chapters in American history. Ms. Haspel needs to explain the nature and extent of her involvement in the CIA's interrogation program during the confirmation process," said Republican Sen. John McCain of Arizona, who was tortured himself as a prisoner of war in Vietnam, said in a statement.

"She'll have to answer for that period of time, but I think she's a highly qualified person," Sen. Lindsey Graham, a South Carolina Republican, told CNN. "That was an authorized program at the time, that would no longer be legal. The problem I would have is if she somehow tried to suggest you could still do that."

Graham was referencing his and McCain's successful push in 2015 for a formal ban across the US government on the use of waterboarding and other techniques that aren't in the Army Field Manual for interrogations, which made the Bush-era tactics illegal.

Maine Sen. Susan Collins, a moderate Republican on the Senate Intelligence Committee, said there will be questions raised about Haspel's nomination, but said she's not going to decide how she'll vote until after the confirmation hearing.

"She certainly has the expertise and experience as a 30-year employee of the agency," Collins said. "But I'm sure there are going to be some questions raised."

Several Democrats were quick to criticize Haspel's nomination after Trump announced he was elevating her to potentially be the first female director of the CIA.

Sen. Ron Wyden, an Oregon Democrat, said her role overseeing the waterboarding of detainees and destruction of CIA tapes was "troubling." Wyden, as well as the American Civil Liberties Union, called for Haspel's CIA records to be declassified as part of her nomination.

"I believe that this information about her involvement (in the interrogation program) should be declassified, and in effect it's been a cover-up that it hasn't been," Wyden said. "This information ought to be made public."

The New York Times reported that Haspel oversaw the interrogation of a terror detainee at a prison in Thailand in 2002.

Haspel was Jose Rodriguez's chief of staff when he ran the CIA's Counterterrorism Center, according to former CIA officials. In Rodriguez's memoir, "Hard Measures," he wrote that he asked Haspel to prepare a cable granting permission to destroy tapes with an industrial shredder of the interrogation sessions of terror detainees, including Abu Zubaydah, an Al Qaeda suspect who was waterboarded while in CIA custody, according to a Senate report. However, Rodriguez said he personally sent the cable.

Not all Democrats are ready to oppose her nomination.

Sen. Dianne Feinstein — who was Senate Intelligence chairwoman in 2014 for the committee's massive 6,000-page report on the Bush-era interrogation programs — had some praise for Haspel on Tuesday, though she said she was not going to decide on her nomination until after the confirmation hearing.

"We've had a long personal talk," she said of Haspel and the interrogation program. "I have spent some time with her. We have had dinner together. We have talked. Everything I know is that she has been a good deputy director of the CIA."

Sen. Bill Nelson, a Florida Democrat, defended Haspel's actions in Thailand, saying it was "the accepted practice of the day" and it shouldn't disqualify her.

"As a 30-year professional in the CIA, I have much more comfort in that than putting someone in who is a politician," Nelson said.

Several top Republicans, including Senate Intelligence Chairman Richard Burr, said they were supporting Haspel's nomination. Several Republicans questioned Democrats' motives in opposing her.

"I can't believe somebody is talking about blocking the first female director of the CIA after 30 years of distinguished service," said Texas Sen. John Cornyn, the Senate's No. 2 Republican. "I find that impossible."

Virginia Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee, said he had a good relationship with Haspel as deputy director, but he noted there were a number of legitimate questions she had to answer.

"I've had a good working relationship with her over the past year, but rightfully there are a lot of questions to be asked," Warner said.

Warner did appear to throw some support behind the efforts from Wyden and the ACLU to declassify Haspel's records as part of her confirmation. When asked if that should happen, he said: "The more transparency the better."