Abraham Lincoln left to Barack Obama not only an example to emulate but also the sentinels who will safeguard his life. In 1865, on the very day he was assassinated at Ford's Theatre, Lincoln green-lighted what would become the U.S. Secret Service, which has been guarding Obama (code-named "Renegade") since May 2007--longer than any other presidential candidate in U.S. history.
The agency's mission has evolved dramatically since its inception under the Treasury Dept. While today more than 3,200 Secret Service members stand ready to sacrifice their lives for the safety of the leader of the free world, the agency's job originally was to stamp out counterfeiting in an era when one out of every three bills in circulation was fake. Though the Secret Service was tasked with guarding President Grover Cleveland's family in the 1890s, presidential security became a formal objective only after the assassination of President William McKinley in 1901. It wasn't until 1951--after a failed attempt on President Harry Truman's life--that Congress codified the agency's permanent protection of the First Family. Its duties also now include candidates for high office and visiting dignitaries. (See the Top 10 secret service code names.)
Scanning crowds while the President walks a rope line is a given. But agents have also had to respond to unique security challenges--from rigging traffic lights while Truman strolled through Washington to shielding President Jimmy Carter's daughter, Amy, from a charging elephant at a pet show on Ethel Kennedy's Virginia estate. While the demeanor (sunglasses, earpieces, constant vigilance) and the danger are what captivate the public, monitoring for fiscal malfeasance is still half the job. In August, the Secret Service helped crack what was heralded as the largest identity-theft ring in U.S. history.