Marc Ambinder (@marcambinder) is an author and journalist based in Los Angeles. He is a former White House correspondent for National Journal, politics editor for The Atlantic, and chief political consultant to CBS News. He is working on a book about nuclear brinksmanship in the Cold War.

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.