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May 8, 2018, 2:53 AM UTC / Updated May 8, 2018, 3:16 AM UTC

A key Democratic senator said he would not vote for Gina Haspel, Donald Trump's pick for CIA director, after a meeting Monday at which she failed to satisfactorily answer questions about her background in the agency, an aide said.

The meeting with Sen. Martin Heinrich, D-N.M., a member of the Senate intelligence committee, took place in a secure space with classified documents two days ahead of Haspel's confirmation hearing on Capitol Hill.

"This is about trust, and the public is not being afforded an open and honest debate about the nominee," Heinrich said after the meeting. "There are questions that absolutely need to be answered publicly, and given her position, she can make the choice to do so. As the nominee, she owes that to the public."

"If these answers aren't going to be provided to the public, how can we trust that the nominee will be open to oversight and accountability?" he asked.

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The committee's vote has not yet been scheduled.

Haspel, a career operations officer who is the agency's deputy director, considered withdrawing her nomination last week amid concerns over her role in the CIA's use of harsh interrogation techniques, officials told NBC News.

Haspel was once the base chief at a secret prison in Thailand where an al Qaeda detainee was waterboarded and confined to a box, several officials have told NBC News.

Haspel later wrote a cable that included an order from her boss instructing CIA officers to shred video of interrogation sessions.

In a statement in March announcing his opposition to Haspel's nomination, Sen. Rand Paul, R-Ky., said that her role at the prison should "disqualify" her from the director's job. Sen. John McCain, R-Ariz., has also questioned her role in using "enhanced interrogation."

It's unclear how many members of the intelligence committee will support Haspel, but she was meeting with senators before her hearing on Wednesday to address concerns.

Sen. Angus King, I-Maine, said he still has questions even after meeting with Haspel. He said he's waiting to see what she says at her hearing.

If Paul maintains his opposition and McCain is absent, at least one Democrat must support Haspel for her confirmation to pass.

Losing the support of key Democrats like Heinrich makes Haspel's prospects for confirmation more daunting. Heinrich and other Democrats have sought to declassify CIA documents that could help clarify her work at the agency.

But the chairman of the intelligence committee, Sen. Richard Burr, R-N.C., pushed back against such requests on Monday, calling them "a comfortable tool for them to hide behind."