I actually think the major television networks are the most responsible for alot of this partisan cable shows.Viewers were driven from their shows in droves because of the slant. Shows like Law and Order would throw their shots every chance they had. Years ago I would watch Johnny Carson before retiring to bed. Then Jay Leno comes out with his monologues consisting of hateful George Bush Jokes. Funny, he didn't do many Obama jokes when is got elected.
The major TV shows lost their audience and most are gone now replaced by reality shows. Good drama is hard to find on TV.
The point I'm making is that partisan cable shows filled a void created by the major networks. Heck, the few times I turn on the television is for sports or Turner Classic Movies. I confess that will will watch Bill O'Reilly once in awhile.