Kweisi Mfume, the president and chief executive officer of the National Association for the Advancement of Colored People, will step down Jan. 1 to pursue new opportunities in the media, politics, and business. Mr. Mfume, 56, who has led the Baltimore-based civil rights organization since 1996, announced his resignation Nov. 30. Dennis Hayes, the NAACP’s general counsel, will serve as its interim president and CEO while a national search for a replacement is conducted.