From TV Guide:
"Rocker Jon Bon Jovi appears as himself and campaigns for an exhausted Santos, who's showing signs of strain during a frantic flurry of campaigning on Halloween. Meanwhile, Toby faces an indictment just days before the election."
Cast Listing: Richard Schiff, Allison Janney, Bradley Whitford, Stockard Channing, Janel Moloney, Kristin Chenoweth, Jon Bon Jovi, Janeane Garofalo, Jimmy Smits, Teri Polo, Ramon DeOcampo, Alan Alda"
More info on Jon Bon Jovi's appearance here.