Magruder moved to Chicago for his MBA studies. Afterward he shifted from IBM to the consulting firm Booz Allen Hamilton. In Chicago he remained involved with the Republican Party. His first major political job was managing the successful 1962 primary campaign of Donald Rumsfeld for the Republican nomination to the United States House of Representatives, preparing for the election in Illinois' 13th congressional district. Rumsfeld won the primary and the seat in Congress, in a major upset in a ward traditionally dominated by Democrats and unions. The win catapulted Magruder into the early ranks of young political technocrats who used data and analytics to engineer campaigns, and it caught the attention of the Republican party machine.