It's become accepted — because it's been repeated by corporate media so often — that PBS and NPR and their local affiliates are left-leaning. It may be true of some of the local affiliates, though demonstrated in ways so small as to be irrelevant. It is not true of NPR and PBS, so fearful that the Right Wing will slash their funding that they cower before it. A recent case:
After corporate pundits concluded that the troubled rollout of the Affordable Care Act called into question the Liberal Democratic philosophy that an activist government can solve big, complex social problems, PBS decided to have a discussion of the matter. Featuring experts from all sides, of course, the PBS way. The media review Extra! described the PBS arrangement. Representative of the left was Wall Street Democrat Steven Rattner, who's worked for major banks and currently runs his own investment firm. He noted the "need to address the issue of spending on Medicare and Social Security."
"From the right, viewers got Douglas Holtz-Eakin, a former McCain economics adviser who is currently helping corporations lobby against tax hikes. But someone at PBS thought viewers needed one more voice from the right, so they added Romina Boccia of the Heritage Foundation. So the spectrum of debate was right, righter and Wall Street." The New York Times, no left-wing organ itself, was moved to note that public television "was created to expand the parameters of public discussion." It's not doing a good job.
Count how many times Sen. Ted Cruz (Tea Party, Texas) appears on the public television and radio networks. Count how many times Sen. Bernie Sanders (Ind., Vermont) does.