Marc Ambinder is a senior fellow at the USC Annenberg Center for Communication Leadership and Policy. A former White House correspondent and political reporter, he is the author of several books about national security, including The Brink: President Reagan and the Nuclear War Scare of 1983. He is a consultant for Spycraft Entertainment and lives in Los Angeles.

Secret Service

The agent tasked with securing the Atlanta site where an armed civilian rode an elevator with Obama has one of the toughest jobs in the agency. What goes into protecting the president.