The idea of the 'Liberal Media' bias started, or at least its being as much of an idea as it is in America today started, with the Nixon era and is very much a Nixonian thought.
In the early 1970s, Nixon discussed the creation of a Conservative news network, one which Agnew could be sent off to and which would shore up support for the administration. This didn't come to fruition. One of the people attached to this idea was Roger Ailes, who later went on to create Fox News.
What if Nixon, or rather his supporters working for Nixon, started a Conservative news network in the 1970s?