WASHINGTON (CNN) -- As President Barack Obama's pick for CIA director heads to Capitol Hill for his confirmation hearing Thursday, some in the president's own party are threatening to hold up John Brennan's nomination.
Oregon Democratic Sen. Ron Wyden told reporters he would "pull out all the stops" to get answers about the legality of targeting Americans involved with al Qaeda overseas. Wyden was not satisfied with a confidential Justice Department memo that was sent to key congressional committees last year but only became public on Tuesday.
The 16-page white paper indicated the U.S. government could use lethal force against an American citizen overseas if the person is a senior operational leader of al Qaeda or one of its affiliates and an attack is imminent. But it was a policy paper rather than the official legal document, which the American Civil Liberties Union says is 50 pages long.
The U.S. drone campaign against al Qaeda and its allies has been one of Brennan's biggest legacies in the four years he has served as Obama's chief counterterrorism adviser.
According to a count by the public policy group New America Foundation, at least 28 of al Qaeda's leading members have been killed in drone strikes -- including the U.S. citizen Anwar al-Awlaki, who played an operational role in al Qaeda in the Arabian Peninsula.
Debate over key question
One of the questions the committee submitted to Brennan in advance of the hearing asked how it was determined that an individual was associated with al Qaeda and that a threat was imminent to justify military force. The question did not distinguish between Americans and others.
Brennan responded in writing that those determinations were made on a "case by case basis through a coordinated interagency process."
Christopher Anders, the ACLU's senior legislative counsel told CNN: "Sen. Wyden was trying to find out that very basic information and has been denied that. So you know the most basic questions about a program that John Brennan has been the architect of and the orchestrator of for four years, the most basic details of it have been withheld."
But late Wednesday, an administration official said some lawmakers will have access to a Justice Department legal opinion on the policy.
"As part of the President's ongoing commitment to consult with Congress on national security matters, the President directed the Department of Justice to provide the Congressional intelligence committees access to classified Office of Legal Counsel advice related to the subject of the Department of Justice white paper," the official said. The president, it was said, is turning over the information because he believes the scrutiny and debate is healthy.
Amnesty International weighed in on the debate, saying Congress should grill Brennan on his claim that the Obama administration's drone strikes are "conducted in full compliance with the law."
"Furthermore, Congress should immediately hold public hearings with independent experts to examine the administration's legal reasoning and ensure that the administration is following the 'rule book' for the use of lethal force that already exists: international human rights law and, in the very narrow circumstances to which it applies, international humanitarian law," the group said.
Other controversies at hand
But there are other controversies Brennan faces at his confirmation hearing.
There is his role in administration leaks about covert operations like the so-called STUXNET cyberattack on Iran's nuclear program and a foiled al Qaeda bomb plot in Yemen involving a mole.
Brennan acknowledged in his written responses to committee questions that he voluntarily was interviewed by prosecutors about those two leaked investigations. He said in both cases his counsel told him he was only a witness in those probes, not a target.
Senators also want to know what he knew about harsh interrogation techniques used on suspected terrorists when he was at the CIA during the George W. Bush years.
Brennan, who was the deputy executive director of the agency at the time, said in his written responses that he "was aware of the program, but did not play a role in its creation, execution or oversight." He also said he privately discussed his objections to some of the program with some of his colleagues.
Brennan promised "these techniques would not be used again by the CIA if I were the Director."
Sen. John McCain, R-Arizona, said last month there have been contradictions in some of Brennan's statements.
"He says that he had opposed 'enhanced interrogations,' or torture, but there are statements that clearly he made several years ago where he supported it," McCain said. "I'd like to see that issue resolved."
Brennan acknowledged in the questionnaire that he still needed to review the conclusions of the committee's 6,000-page classified report on the agency's detention and interrogation program before the hearing, and he may be asked to elaborate further on his response to a question about whether he thought coercive interrogations were "effective in producing reliable intelligence that saved lives."
Although Brennan said he opposed the enhanced interrogation techniques, "a lot of information, both accurate and inaccurate, came out of interrogation sessions conducted by the CIA, including those where EITs were employed."
Brennan says he's ready to lead the CIA
Outrage over the interrogation program scuttled Brennan's chances to lead the CIA in Obama's first term. But now he says he is ready for the political heat.
When Obama nominated him for CIA director last month, Brennan said, "Although I consider myself neither a Republican nor a Democrat, I very much look forward to working closely with those on both sides of the aisle."
As the president's top counterterrorism aide, Brennan continues to be seen as all-powerful.
"I do think John is regarded in terms of the intelligence community, even where he is now, as the first among equals," CNN national security contributor Frances Fragos Townsend said.
As CIA director, Brennan would report to James Clapper, the director of national intelligence. But when there's a call for highly secretive covert action, he would have a direct path to the president, talking to him on the phone or walking right into the Oval Office to brief him.
"While the CIA director will keep the director of national intelligence apprised of what he is doing, it is actually the direct responsibility of the CIA director to respond to the president in terms of covert action," Townsend said.
She added that she doesn't foresee a problem because of their long-term relationship. "They know each other, they respect each other and I think they like each other."
As for the confirmation hearing, expect to see some Washington drama, but no state secrets revealed. Any discussion of intelligence crown jewels will happen afterward in a closed-door, classified session.
CNN's Tom Dunlavey and Lesa Jansen contributed to this report.