Conversation so far:
What did Brennan do as an advisor to Obama?
In late 2008, Brennan was reportedly the top choice to become the next Director of the CIA in the incoming Obama administration.
When did he begin in that position?
President Obama then appointed him to be his Deputy National Security Advisor for Homeland Security and Counterterrorism.
What else did he do?
In August 2009, Brennan criticized some Bush-administration anti-terror policies, saying that waterboarding had threatened national security by increasing the recruitment of terrorists.
Did he have any notable moments under Obama?
Brennan was present in the Situation Room in May 2011 when the United States conducted the military operation that killed Osama bin Laden.

Question: What else is significant?
Self-contained rewrite: Besides criticizing some Bush-Administration anti-terror policies and being present in the Situation Room in May 2011 when the U.S. conducted the military operation that killed Osama bin Laden, what else is significant about John Brennan?