CIA director nominee John Brennan weathered a barrage of probing questions Thursday, as lawmakers pressed for more information about the administration's rationale for drone strikes against Americans -- with his confirmation potentially hanging in the balance.
Lawmakers, after threatening a "confrontation" earlier this week over President Obama's nominees unless they get access to key drone documents, used Brennan's confirmation hearing before the Senate Intelligence Committee to air long-simmering concerns about the issue.
Earlier in the day, senators were allowed to review some of the legal rationale -- released in a bid by the Obama administration to tamp down the controversy. But top Democratic lawmakers said Thursday afternoon they want more, as Brennan repeatedly defended the program itself.
"It's the idea of giving any president unfettered power to kill an American without checks and balances that's so troubling," Sen. Ron Wyden, D-Ore., said. "Every American has the right to know when their government believes it's allowed to kill them."
Wyden said he's concerned the Justice Department is "not following through" on providing "any and all" opinions -- aside from what was provided Thursday morning.
As he did with other senators, Brennan vowed to do what he could to pry loose that information. Brennan also said it's important to speak publicly about the rationale, saying "people are reacting to a lot of falsehoods that are out there."
"We only take such actions as a last resort to save lives when there's no other alternative," he said, claiming drone strikes are not ordered to punish terrorists for past attacks.
Brennan faced bipartisan scrutiny Thursday, with Democrats pressing him on drones and his views on Bush-era interrogation tactics. Republicans, meanwhile, repeatedly questioned him on his knowledge of high-profile security leaks last year. Brennan has acknowledged being interviewed as part of an investigation into those leaks, but said Thursday he is not a target of that investigation.
One lawmaker, Sen. Richard Burr, R-N.C., further threatened to hold up the confirmation over an another issue -- the release of separate documents pertaining to the Benghazi terror attacks.
On the drones, Committee Chairwoman Dianne Feinstein, D-Calif., complained that, after lawmakers were allowed by the administration to view the classified drone document earlier in the day, "our staff was banned from seeing it."
"This is upsetting to a number of members," she said.
Feinstein tried to get Brennan to commit to, if confirmed, working to provide eight additional legal opinions about drone strikes.
Brennan sought to ease lawmakers' concerns. He said Thursday that being confirmed to the post would be "the greatest honor of my professional life."
He also said he understands the "great interest" in the legal basis used for killings outside the battlefield of Afghanistan. He voiced interest in promoting public discussion on it.
"Our system of government and our commitment to transparency deserves nothing less," he said.
Brennan is described as the public face and architect of the targeted-killing program, which has expanded under Obama. Under Brennan, the American cleric Anwar al-Awlaki, considered a top Al Qaeda operative, became the first American successfully targeted for death under the program. Two weeks later, his 16-year-old son was also killed in a drone strike, in which the teen was described as collateral damage.
The start of Brennan's hearing was interrupted several times by protesters from Code Pink. Feinstein briefly suspended the hearing while the protesters were cleared from the room.
As the hearing resumed, Brennan also faced continued questions about his views on Bush-era interrogation tactics -- which included waterboarding.
In an interview with CBS News in 2007, Brennan defended the program as one that has produced information that's been "used against the real hardcore terrorists."
Brennan has since taken a position against the program and claimed he raised concerns while at the agency. He reiterated that point Thursday, saying he raised "personal objections" to it, but did not try to stop the program -- something he said was run by other parts of the agency. He also called waterboarding "reprehensible."
A former deputy director at the agency could not confirm, in an interview with Fox News, that Brennan raised concerns with him. Still, the official, John E. McLaughlin, said he supports Brennan's confirmation and he should be taken at his word.
"This was not a program that would normally be discussed between John and myself, but if he said he talked to colleagues about it, and expressed reservations, I believe him, because this is a very straight-forward, honest guy," McLaughlin told Fox News.
Meanwhile, Feinstein has completed a 6,000-page classified report on the CIA program. Those familiar with its findings tell Fox News it concludes the agency lied about the program's effectiveness -- a charge denied by those who ran the program. Brennan was asked about that report Thursday, and said he found some elements of the report "disturbing."
On Wednesday, White House Press Secretary Jay Carney defended the nominee.
"The president believes that John Brennan is uniquely qualified as a 25-year veteran of intelligence work, a 25-year veteran of the CIA, to lead that agency," Carney said. "Mr. Brennan brings, I think, not only a vast amount of experience, but a significant perspective on the battles that we wage in this effort and the right way to conduct them."
Carney said Obama wants the Senate to confirm him "expeditiously."
Fox News' Catherine Herridge contributed to this report.