The problem with a biased MSM is that it gives Dems a pronounced advantage among low information voters. The vast majority of folks who bother to watch cable news have already made up their minds, and are relatively well informed (at least as compared to the folks who get their news predominately from E!).
The persuadable low information voters are who the parties are gunning for, and these people just don't pay much attention to news. They get their news in dribs and drabs - a snippet from the morning shows, entertainment/gossip/reality shows, the occasional newspaper or magazine front page sitting in the hotel, restaurant, or waiting room. These media are dominated by liberals. Maybe they'll tune in to one or two of the presidential debates, moderated by - you guessed it - liberals. In the second debate, for example, between Romney and Obama, Candy Crowley did Romney a severe disservice by "fact checking" one of his statements about Benghazi - a statement that was true. Crowley acknowledged her mistake the next day, but the damage was done.
So while FoxNews and talk radio provide nice alternatives for conservatives, they don't have much effect in persuading the low information voters. Fox's biggest impact is occasionally shaming the other networks into providing more coverage of stories they would rather ignore. Stories like Benghazi and the Goznell serial killer abortionist, for example.
