Two top Republican senators are warning they may oppose Chief Counterterrorism Advisor John Brennan as President Obama's pick to head the CIA.

Sen. Lindsey Graham, R-S.C., and Sen. John McCain, R-Ariz., are demanding answers from the Obama administration over the Sept. 11 attack on U.S. Consulate in Benghazi, Libya.

Graham said Sunday he and McCain "are hell-bent on making sure the American people understand" how four Americans could have been murdered at the consulate.

"I'm trying to find out what happened on that night so we won't have other Benghazis, and I'm not going to vote for Brennan until the CIA … lets us know who did it and why and we have a picture of what happened in real-time," Graham warned.

The Senate Intelligence Committee is scheduled to vote early this week on Brennan's nomination for CIA director.

Sign the Christian Coalition's "Demand the Truth About Benghazi" Petition Today!