Scott Adams put forward the idea that what we are perceiving as an impossible persistence of nonjournalism due to bias may actually have a different cause. Intelligence agencies and other government entities have slowly and quietly taken over news outlets as their house organs. While journalists do collect some information from other sources and pursue stories in the old way, this is just an allowed cover activity. The bulk of their info is "leaked" to them in carefully curated ways. We have trouble perceiving this because we start from a zero point of what journalism should look like and what fairness is. But that may be long ago. The various outlets have long ago been steered into depending on government sources as their primary food.
It has long been understood by people willing to look on it with a steely eye that the Washington Post is the house organ of many government agencies, and interestingly, ones that do not always have the same goals. The Post has embraced this role. We have long wondered if that is mostly true, how much is that true of other outlets? I think Adams is not suggesting anything new. He is saying "Whatever you previous estimate was, consider doubling it. And how would you know or measure it anyway? The skill set of intelligence agencies is to influence governments. Why not ours?"
It's easy to treat this with as mere cynicism. Even if not true, it may be truer than we have heretofore credited. Maybe we can't undermine the political bias and push it back because bias isn't the real enemy. We punch the air. Those of us who think in terms of issues and fairness and history tend to think that those must be the factors in play, but others have them badly wrong. Liberal bias may be real but only a moderately important aspect of what's happening.
Update: James notes a parallel process in the bias toward foundations that fund media sources. Link in the comments.