After forming an exploratory committee in June 2005, Paccione announced, in September 2005, her intention to challenge two-term incumbent Republican Marilyn Musgrave for Colorado's Fourth Congressional District, in what evolved into a highly competitive battle the Cook Report rated a "toss-up" race for the historically Republican seat. In September, the race was designated as a third-tier pickup opportunity for Democrats by the Democratic Congressional Campaign Committee, which provided $70,000 to the Paccione campaign for direct mail advertising. Paccione was endorsed by the "Denver Post".