Which of the following Presidents of the United States was assassinated?

The story behind the answer

William McKinley was assassinated in 1901 when anarchist Leon Czolgosz shot him during a public reception at the Pan-American Exposition in Buffalo; he died days later from infection. His killing prompted the Secret Service to begin protecting presidents full-time.

A handy memory aid: the four assassinated U.S. presidents follow L-G-M-K—Lincoln (1865), Garfield (1881), McKinley (1901), Kennedy (1963). In contrast, Franklin D. Roosevelt died of a cerebral hemorrhage in 1945, Lyndon B. Johnson of a heart attack in 1973, and Chester A. Arthur (who became president after Garfield’s assassination) died of kidney disease after leaving office.