Keenan's political career began with an internship in the mailroom of Ted Kennedy's senate office in 2003, before going on to become the senator's legislative aide. After a stint as a staff assistant for the Senate Health, Education, Labor and Pensions Committee, Keenan took a master's degree in public policy at the John F. Kennedy School of Government, studying speechwriting and delivery under Steve Jarding. In 2007, Keenan took a summer internship in speechwriting on Barack Obama's presidential campaign, working under Jon Favreau, before returning to the Kennedy School to complete the second year of his studies. He remained involved in the campaign during the year, flying to Iowa during the Christmas break to assist in preparation for the Iowa caucuses. After Hillary Clinton conceded in June 2008, Keenan returned as a full-time staffer on Obama's presidential campaign.