The Democratic primary took place on September 8, 1920. Incumbent U.S. Senator Marcus A. Smith was the recipient of a significant challenge in the Democratic primary, notably by Maricopa County Superior Court judge Rawghlie Clement Stanford, who would go on to become Arizona's fifth Governor in 1937. Fellow lawyer Albinus A. Worsley, as well as John W. Norton also ran in the primary. Smith narrowly staved off his primary challengers and went on to compete in the general election in November.