In White House councils, John Brennan has been privy to the most secret U.S. intelligence programs. Outwardly, he has been the administration's most public defender of one of President Barack Obama's most controversial practices - the expanded use of armed drone aircraft to kill terrorism suspects overseas.  This is the second time that Obama has sought to put Brennan at the helm of the CIA, and his confirmation process is likely to revisit old controversies over U.S. counterterrorism measures undertaken by the administrations of Obama and George W. Bush.