NEW : President riffs on news networks , Jay-Z , Jay-Z . NEW : Obama shifts to somber note in talking about tragedies in Boston , D.C. . NEW : Kevin Spacey comes up with dream D.C. movie cast . NEW : Conan O'Brien speaks as Congress character .
NEW : President riffs on news networks , Jay-Z , hairdo . NEW : Obama shifts to somber note in talking about tragedies in Boston , Texas . NEW : Conan O'Brien comes up with dream D.C. movie cast . NEW : Kevin Spacey speaks as `` House of Cards '' character .