Presidential debate (6 p.m. CNN): Democrats debate in Los Angeles.
College basketball (7 p.m., Ch. 14): Idaho State at Weber State
Smallville (7 p.m., Ch. 30): Bizarro poses as Clark (who's frozen in the Fortress of Solitude).
Supernatural (8 p.m., Ch. 30): Sam and Dean take on a coven of witches.