Since 1972 and on an annual basis since 1997 (excluding 2006), Gallup has asked Americans the following question:
"In general, how much trust and confidence do you have in the mass media - such as newspapers, TV and radio - when it comes to reporting the news fully, accurately and fairly - a great deal, a fair amount, not very much or none at all?"
Here is a history of the percentage of Americans that answered "a great deal or a fair amount of trust and confidence" since 1997:
Americans' trust in their media peaked in 1976 at 72 percent, largely on the basis of actual investigative journalism that was done during the Watergate/Nixon scandal and the Vietnam war. By 1997, confidence had dropped to 53 percent and, with the exception of 2004, remained above 50 percent until 2005. Since then, Americans trust in their own media has dropped from 47 percent in 2007 to only 32 percent in 2016, an all-time low.
Let's look at how political affiliation affects trust in the media, much of which is generally regarded as "liberal friendly". Here is a graph showing the trust in mass media (either a great deal of trust or a fair amount of trust) by party affiliation since 1997:
In general, Republicans tend to have significantly less trust in America's mass media than Democrats with differences peaking at 39 percentage points in 2005 although it should be noted that the 37 percentage point difference in 2016 is not far behind. Democrats' trust in mass media peaked at 70 percent in 2005 and reached its low point of 51 percent in 2016. Republicans' trust in mass media peaked at 52 percent in 1998 and reached its low point of 14 percent in 2016, a level that is 13 percentage points below its previous low of 26 percent seen in 2012. It is interesting to observe that during the 2000 election year when George W. Bush was running against Al Gore, there was only 6 percentage points separating the Republicans and Democrats, the lowest difference in the 20 year annual history of the poll. Since that point, Republicans' trust in mass media has declined from the high 40s to the lower- to mid-30s/high 20s. Over the same timeframe, Democrats' trust in mass actually rose to a high of 70 percent as noted above, then fell relatively rapidly to the mid- to high-50s.
I think that it is even more interesting to look at how the percentage of Americans that have no trust whatsoever in America's mass media has increased since 1997. Here is a graph showing the growing percentage of Americans who answered Gallup's question with a "none at all" response:
It is interesting to observe that complete distrust in mass media has tripled to 27 percent in 2016 from its low point of only 9 percent in 1998. This is a strong statement about the validity of the mainstream media today since this has been the traditional source of news for most Americans.
While it is quite obvious that the divisiveness of the 2016 presidential election has led to a significant drop in the "trust quotient" for Republicans, the significant decline in the percentage of all Americans who either trust or mainly trust the media is significant and, even more significant is the tripling of Americans who have no trust at all in what is offered to them in the form of "news". A great deal of this has to do with the growth of the 24 hour news cycle where networks are forced to fill long periods of time with so-called "news items", much of which takes the form of idle chit-chat. The decline in trust can also be connected to the lack of original investigative journalism and the rise of opinion journalism which really isn't journalism at all.