there's a factor this does not seem to capture well, and i only notice because i see npr near the top and center. the factor that's missing might be called "manipulation by omission", or something.
i listened to npr pretty much exclusively for news for years leading up to the 2016 election, for the reasons implied by this chart and also because some of the non-news content appealed to me. but when that election cycle started gearing up, i realized i was repulsed by hilary clinton, and interested in understanding bernie sanders in a fuller way before deciding how to deal with my vote. then a funny thing happened. bernie, who had been getting plenty of coverage for non campaign matters, disappeared from npr. hilary was omnipresent. almost as omnipresent as...trump. it was a idiotic as a hollywood hero movie. the strategy of highlighting only one democrat candidate, while putting the brightest spotlight of all on a ridiculously caricatured straw man as her opponent, while excluding all coverage of any other serious candidate on either side....it all just crystalized then for me, and i haven't listened to npr since. the richest irony is that all of the left leaning media seemed to do this, believing they could cash in on the spectacle of trump for traffic without risking any vulnerability in the election. but as some obscure writer said in the first century, "you cannot worship god and mammon". cash won, and as a consequence, so did trump. thanks a lot, liberal media, for giving us trump.