Being a Secret Service agent is one of the most treacherous jobs in the world and never more so than in today's highly polarized America. Facing threats from fence jumpers and manifesto writers, and from fanatical terrorists and sophisticated spies, protecting the president is harder than ever. In an age of hyper-partisan politics, emotions are high and crazies are a dime a dozen. On top of that, with international tensions reaching a boiling point,...