in 1991, mcmahon co-founded the media consulting firm trippi mcmahon and squier with mark squier and joe trippi. mcmahon's early work for the firm included a role as media strategist for california governor jerry brown's 1992 presidential campaign. throughout the 1990s and 2000s, mcmahon and his partners worked on all five of howard dean's gubernatorial campaigns. mcmahon was also a strategist and consultant for dean's 2004 campaign for the us presidency. following dean's departure from the race, mcmahon's firm served as the lead advertising partner for the media fund, which produced ads in support of then-senator john kerry's presidential campaign. after the 2004 presidential election, mcmahon worked on dean's successful 2005 campaign for chairman of the democratic national committee.