What was the motif for the assassination of James Garfield?

James A. Garfield was shot in Washington, D.C. on July 2nd, 1881 at 9:30am. His assassin was Charles J. Guiteau who believed that an essay he had written was responsible for Garfield's victory. Guiteau demanded a diplomatic post for his services, but was denied the position. Garfield then set out to kill the ungrateful president. Garfield died eleven weeks later from the wound on September 19th, 1881, less than four months after taking office as the 20th President of the United States. Garfield became the 2nd president to be assassinated.