It was because of the McKinley assassination that the U.S. Secret Service began protecting presidents. William McKinley, our 25th president, was shaking hands at a fair in Buffalo, NY on September 5, 1901, when anarchist Leon Czolgosz shot him twice in the stomach. At first, McKinley's wounds were thought to be minor; his VP, Teddy Roosevelt, went on vacation the next day. In reality, the president's stomach was rife with gangrene and the lingering infection killed him nine days later. (Czolgosz was later executed.) Though he was the only one implicated in the assassination, some historians believe that Czolgosz was part of a larger conspiracy of anarchists.