While White House counterterrorism adviser John Brennan's nomination to lead the CIA has already stirred up questions about his role in the government's interrogation and drone programs, another controversy is likely to follow him into his confirmation hearing -- the explosive battle over security leaks last summer.
For months, Justice Department attorneys have been investigating who leaked details to the press about cyberattacks on Iran and an Al Qaeda plot to place a bomb on a U.S.-bound jet. Those leaks, along with the drip-drip of information about the Usama bin Laden raid and the U.S. drone program, prompted accusations last year that the Obama administration was strategically releasing sensitive information to make President Obama look good in an election year.
Brennan was never directly accused of leaking those details, and last summer he even condemned some of the leaks as "devastating."
But some lawmakers aren't convinced Brennan, as the top White House adviser on counterterrorism matters, is in the clear either.
"To our knowledge, John Brennan has not been absolved of responsibility for the high-level national security leaks that have characterized this White House," an aide to Sen. John Cornyn, R-Texas, told FoxNews.com, noting the senator has "some concern" about the issue.
Sen. John McCain, R-Ariz., has also raised questions about whether Brennan bears some responsibility for sensitive security details leaked to the media.
Brennan, as he has been for the past four years, was in the top tier of Obama's security advisers at the time of the leaks.
Last July, then-House Judiciary Committee Chairman Lamar Smith, R-Texas, included Brennan on a list of top administration officials he wanted to interview on the issue. Shortly before that, more than 30 Republican senators wrote a letter suggesting National Security Adviser Tom Donilon was a possible source.
A May 2012 Reuters story also raised the question of whether Brennan may have inadvertently tipped off the media to a supposed mole inside Al Qaeda in the Arabian Peninsula. At the time, Brennan reportedly said on a private teleconference that Washington had "inside control" over an AQAP bomb plot. Shortly afterward, one person on that call repeated the claim on ABC News. But the White House noted at the time that the Associated Press originally broke the story - Brennan was reportedly called in just to handle damage control.
Last summer, Obama said the idea that the White House would intentionally release any sensitive security information was "offensive" and "wrong."
Brennan himself criticized the leaks during an address last August, while slamming accusations that the leaks were political as "highly irresponsible."
At the time, Republican Rep. Peter King was among those who claimed the administration was trying to "build up" the president's reputation with the leaks before November.
On CNN Tuesday night, McCain said he has questions about Brennan's comments dating back to the 2011 raid on Usama bin Laden's compound.
"I believe there's also serious questions about the information that Mr. Brennan gave from the White House after the bin Laden raid, such as the identity of Seal Team 6, a story about how they believe bin Laden had reached for a gun ... a number of statements that he made," McCain said.
Foremost, though, McCain has raised concern about how complicit Brennan may have been with the Bush-era enhanced interrogation techniques. While Brennan has condemned waterboarding, a practice McCain also opposes, the Arizona senator said he hasn't "heard anyone say that at the time they heard Mr. Brennan object to the waterboarding and the other techniques."
Brennan's nomination, while controversial, has been overshadowed by the nomination of former Nebraska Sen. Chuck Hagel for secretary of defense. Hagel is facing his own set of questions about past comments that offended gay-rights and pro-Israel groups.
The White House has vigorously defended both nominees. Officials stress that Brennan is a 25-year veteran of the CIA - on Monday, Obama called him one of his "closest advisers."
"John has been tireless. People here in the White House work hard. But John is legendary, even in the White House, for working hard," Obama said, adding that he "has worked to embed our efforts in a strong legal framework."
That argument could be used to counter groups like the American Civil Liberties Union which continue to question Brennan's role in the CIA interrogation methods. The administration has also argued that Brennan is the one who helped end that program after Obama took office.