The Secret Service wasn't always intended to be the president's last, best line of
In the run-up to the 2004 presidential election George W. Bush spoke at Louisiana State University (LSU), where National Geographic took a closer look at the Secret Service for a documentary called "Inside the US Secret Service." The film follows the president's advance team as it worked with local law enforcement to make sure every conceivable threat to the president addressed before he arrived.
National Geographic doesn't spill all the secrets, but what they let us in on is still pretty cool.