For 10 points, name this event in which Leon Czolgosz killed the 25th U.S. President.
This event took place in spite of George Cortelyou's request for extra security at the Temple of Music. An X-ray machine was available, but it was not used to find the fatal bullet, fired by a revolver concealed in an anarchist's handkerchief. This event occurred at the (*) PanAmerican Exposition in Buffalo, New York, and it led to Theodore Roosevelt becoming President. For 10 points, name this event in which Leon Czolgosz killed the 25th U.S. President.
This event took place in spite of George Cortelyou's request for extra security at the Temple of Music.
Assassination of William McKinley (both underlined portions required; accept equivalents; prompt on partial answers)