quote, "shield yourself." go into a house, a basement, a car, and tud difficulties show that will reduce casualties by 50 percent if you do it fast. the question of the moment, how likely is a nuclear attack on the united states and the answer depends on who you ask. we have deputy director of homeland security policy institute at george washington university. great to see you. i'm sorry, but it is just hearing them say "get in a bathtub," after a nuclear bomb, is there anything to this? >>guest: science is improved since "duck and cover," but it could be a failure of communication to think you would survive a bomb blast by jumping into any area that is laughable. the reality is, we should do anything we can to keep ourselves away from the radiation which is a fallout not the explosion itself.