The Young Hipublicans By JOHN COLAPINTO The temptation, upon entering Charles Mitchell's dorm room at Bucknell University, is to assume that he's kidding. The doormat features a picture of Hillary Clinton and the injunction, ''Wipe Liberally.'' A vast American flag festooned in red, white and blue Christmas lights adorns one wall, along with a faded Reagan-Bush '84 poster and a small photograph of the cowboy-hatted Gipper himself. The sole concession to any interest outside right-wing politics is a wall hanging of an African jungle scene. ''My nod,'' says Mitchell, an intense 20-year-old history major, ''to multiculturalism.'' There's an element of...