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.
What else did John O. Brennan do as Deputy National Security Advisor for Homeland Security and Counterterrorism?
John O. Brennan's responsibilities included overseeing plans to protect the country from terrorism and respond to natural disasters, and he met with the president daily.
Did John O. Brennan have any notable moments under Barack Obama?
In February 2010, John O. Brennan claimed he was tired of Republican lawmakers using national security issues as political footballs, and making allegations where they did not know the facts.

Question: What else is significant?
Self-contained rewrite: What else is significant about John O. Brennan and serving as Deputy National Security Advisor for Homeland Security and Counterterrorism to President Barack Obama?