I never considered Breitbart as part of mainstream media, so I ignored that. CNN is in a completely different position than Breitbart.
"Mainstream" used to be NBC, CBS, and ABC, plus AP and UPI. Of those, UPI's gone; NBC, CBS, and ABC have more-or-less abandoned their role. Fox and CNN are new-ish (at least to a person of my age). So to claim that "the mainstream media" all abandoned the center means "almost all the original ones did" - not counting Fox (or even CNN) in the reckoning. Never the less, CNN and Fox are far more mainstream than Breitbart, which is a marginal fringe player.
"Mainstream" used to be NBC, CBS, and ABC, plus AP and UPI. Of those, UPI's gone; NBC, CBS, and ABC have more-or-less abandoned their role. Fox and CNN are new-ish (at least to a person of my age). So to claim that "the mainstream media" all abandoned the center means "almost all the original ones did" - not counting Fox (or even CNN) in the reckoning. Never the less, CNN and Fox are far more mainstream than Breitbart, which is a marginal fringe player.