(CBS News)before the Senate Intelligence Committee on Thursday, and is likely to face mounting scrutiny over the Obama administration's clandestine "drone strike" killing policy.
Late Wednesday night, the White House gave in to growing pressure and released classified information from a Justice Department legal opinion on the targeted killing of American-born terrorists to Congress.
Congressional leaders in both parties have been outspoken in recent days after athat indicates drones can be used more broadly and with less evidence than earlier policies allowed.
Ahead of the hearing, Sen. Susan Collins, R-Me., shared her concern about the secretive policies, saying "in many cases, we are talking about hardened terrorists. But we do need to have a different approach when an American citizen is involved."
Congressional Democrats are also voicing concern, pushing to clarify Brennan's role in the White House-approved drone attacks. On Wednesday, Senator Ron Wyden, D-Ore., threatened to "pull out all the stops" to get the Justice Department memo made public.
CBS News security analyst Juan Zarate said Brennan is likely to face questions "about his past involvement in policies that were controversial during the Bush administration ... he's going to face questions from Democrats about his prior role in detention and rendition policies." He will also have to answer for "the targeting of American citizens, the authority to target with lethal force and what his role and the administration's views are on precisely those policies."
The administration insists that withholding the information is in the best interest of the American public.
"The information that is kept secret is kept secret for national security reasons, not to keep it from the American people," White House spokesperson Jay Carney said Wednesday.
The drone program puts President Obama in a tight spot politically, because as a senator and presidential candidate, he criticized the Bush administration's anti-terrorism policy as a violation of civil liberties. Today, the ACLU is going after the president for what they believe is an example of acting outside of the law.
"We have a president who is doing something that even President Bush didn't do, which is to order the killing of a United States citizen without clear evidence of an immediate attack," Chris Anders of the American Civil Liberties Union told CBS News' Bill Plante.
Zarate added that it was a mistake on Obama's part to release the so-called Bush torture memos in 2009, saying recent revelations indicate "a little bit of hypocrisy here."