Conversation so far:
What did John O. Brennan do as an advisor to Barack Obama?
John O. Brennan served as chief counterterrorism advisor to U.S. President Barack Obama, with the title Deputy National Security Advisor for Homeland Security and Counterterrorism, and Assistant to the President.
When did John O. Brennan begin as Deputy National Security Advisor for Homeland Security and Counterterrorism?
In late 2008.

Question: What else did he do?
Self-contained rewrite: What else did John O. Brennan do as Deputy National Security Advisor for Homeland Security and Counterterrorism?