SEASON FINALE: It’s the last first-run Saturday Night Live installment of the season, a time when the show’s writers and performers simultaneously are wheezing their way to the finish line and marshaling energies for one last great push of inspiration. The week in politics has given no end of inspiration – and with tonight’s show being the last time to play until fall, even pop-in players like Alec Baldwin and Melissa McCarthy are good bets to show up. The guest host is Dwayne Johnson, shown here in a new promo, and the musical guest is Katy Perry, who may even take part in a sketch or two herself.