Naaaah, I don't agree. Trump isn't going to lose any of his support. 99.999% of his supporters don't watch fake news anyway. He has't lost a single person that supported him before, and he won, and in fact he's picked up more support. There's only one way he could possibly lose, and that's for the democrats to cheat, and they're trying very hard to do that. I don't think if Trump tells cnn and the other leftist propaganda wings to go pound sand, it won't make any difference what so ever to his supporters. I wouldn't care, and I highly doubt I'm alone.
Winning elections isn't about your base. Your base will almost always be there because the alternative is much worse.
Winning elections is about convincing the middle you are the better option. The middle are by and large mostly uninformed and watch all types of channels.
For example Trump won the last election because he ventured into democratic areas and stole votes from those who Hillary ignored.
If Trump was dumb enough to alienate half the population in an attempt to spite the media he would deserve the loss