Since retiring from the Senate, he has emerged as a consultant on national security, and continues to speak on a wide range of issues, including the environment and homeland security. In 2006, Hart accepted an endowed professorship at the University of Colorado at Denver. He has been a visiting lecturer at Oxford University, Yale University, and the University of California. He is Chair of the U.S. State Department's International Security Advisory Council, Chair of the U.S. Defense Department's Threat Advisory Council, and Chair of the American Security Project. He was Vice-Chair of the Advisory Council for the U.S. Secretary of Homeland Security, Co-Chair of the U.S.-Russia Commission, Chairman of the Council for a Livable World, and President of Global Green, the U.S. affiliate of Mikhail Gorbachev's environmental foundation. Most notably, he was Co-Chair of the U.S. Commission on National Security for the 21st Century, known as the Hart-Rudman Commission, which predicted terrorist attacks on America before 9/11.