Do politicians manipulate the public via the press, or does the press control politicians via the public?

I believe that media outlets used to have to compete on credibility - a little critical thinking distributed throughout the population made a difference. But with so much consolidation of mass media, especially behind the scenes, one is left picking between only a few fundamental options. If they're all trash, where else are you going to go? It much tougher to take a principled stand and reject all mass media outlets rather than the easy route of identifying with the ones that better stroke your biases.