The Republican base has been primed for this for quite a while; for many years, in fact. These accusations of media bias, liberal media, and brainwashing by academic ideologies is nothing new. The groundwork had been laid for Trump and slowly cultivated year after year. Bush II would frequently accuse the media of bias whenever it reported critically about him. Under Obama they claimed the media were working on his behalf. The same thing occurred under Clinton, they made the same accusations about unsubstantiated media bias. As more and more evidence mounted to discredit the increasingly reactionary policies and ideas of the right wing, the more they'd scream "bias!"
This is one of the really difficult parts of all of this for me. A lot of people seem to be forgetting that this has been building up for quite a while. As someone who is liberal but used to be conservative and still hung out on some conservative places online because of friendships, I constantly saw complaints about the "liberal" "main-stream media." This has been coming for a while, and the blame is not entirely on Trump. He's taken it to a level that is absolutely terrifying, but folks have been trying to discredit "the media" for decades.
That said, a lot of media organizations do have a liberal bias. However, most still try as best they can to be objective, and in a lot of cases, end up going overboard in what they allow to compensate for their bias, in my opinion. That's how Trump managed to get away without being questioned on his lies for so long, and why now that the media is actually calling them out, they're being accused of being biased. They should have been calling out those lies all along, but because they were trying to seem neutral, they let them stand.
