I see two factors at play in the way that the media broadcast news, particularly in the US.
The first is to present news to attract an audience, and in so doing it tends to prefer the sensational over the mundane. It is sensational to find the hidden flaws in any public figure, be that political, in the entertainment business or a sporting figure.
We see in this US election coverage repeated inclusion of Trump's bogus claims without any serious fact checking and we also see this in commentary on Clinton's history since she has been in the political eye for so long and has managed to create a critical eye for many reasons..
The second is the inherent bias in the US media where we have stations such as MSNBC which is clearly a Democratic influenced news source, and Fox News with the added blowhards involved in talk radio who shamelessly promote Republican ideology. They will say anything to undermine any non-Republican, regardless of the truth.
Perhaps a third issue is the ubiquitous presence of social media which is notably not fact checked and more of a rumour mill that users lap up like cream.
Underlying this is the simple fact, perhaps, that neither of the candidates for President are particularly attractive as capable Presidential material but represent either the establishment that has not solved the problems of the middle and lower income classes or the outlandish as a way to break the established order with populist outcries.
Finally,
Fox News is “mainstream" only by the modern and severely diluted definition of the term. Walter Cronkite once pulled audiences in the tens of millions. Fox is watched by 2-3 million people. By any reasonable calculation, Fox News is niche. And its niche is old white men. Cable news is a kingdom lead by elders where Fox News serves as king. The median age of Americans watching CNN, MSNBC, and Fox News is over 60. Half of Fox News viewers are over the age of 68.
Television is particularly popular among men, people who didn’t go to college, and people over the age of 70, which is a great description of a predictable conservative. (Retired seniors watch more than 50 hours of television a week.) Indeed, this older male group is not only ready-made for cable-television-viewing; it comes prepackaged with extremely conservative views. Over the last three general-election cycles, the 65-and-up group voted for the GOP presidential candidate by an average of 9 percentage points.