Hartman attended Minneapolis North High School but dropped out his junior year when he received a lucrative news run for delivering the "Minneapolis Tribune". In 1941, he lost his "Tribune" news run when the Des Moines newspaper magnate John Cowles Sr. bought the Tribune Company. For a brief time, Hartman became a vacuum salesman, but the occupation did not suit him. In his autobiography, Hartman conceded that he was "the world's worst vacuum cleaner salesman." After Pearl Harbor, Hartman attempted to enlist in the United States military during World War II but was rejected because of his asthma.