Both Ryan and Biden held extensive rehearsals, with stand-ins for their opponents.
Biden turned to Rep. Chris Van Hollen, D-Md., who is well-versed in Ryan's policy views from his tenure as senior Democrat on the Budget Committee.
Ryan's foil in rehearsal was former Solicitor General Ted Olson, a skillful courtroom advocate.
Associated Press writers Philip Elliott in Kentucky, Ken Thomas in Florida and Kasie Hunt in North Carolina contributed. Espo reported from Washington.