Most average people outside the "media" which would be a very broad collection of the TV, print media, radio, internet, Hollywood, political and social organizations, etc. in today's communications world don't even know the difference between right and left in the political or social sense. This same 'media' has, perhaps purposely and perhaps without any particular intent or design or motive or agenda, has so skewed and distorted the messages they spew forth that it is difficult for the relatively uninformed or inattentive to really know what's actually going on.
In some cases, the leftist leaning media will hide their agendas and in other cases they are blatantly obvious and do so deliberately.
The 'truth' is no longer important - only the effect created or caused by the message's content. To most left leaning media, the impact of the message on the minds of the targeted audience is all that matters. The effort is to sway public opinion on any given topic to a leftist perspective without regard to any attempt to honestly inform them. The slant is often in the omitted information as much as in the 'facts' included in the story.
The left learned years ago that 'what the public does not know won't hurt the cause to be supported. When the facts honestly are told, a relatively large majority of the public can think sufficiently rationally so as to make reasonably good judgments as what is and is not best for the Nation and the people who live here. Distortion, lies and misrepresentation is the modus operandi of the left. This approach was promoted by the communists and socialists of eastern Europe and Russia for many decades.
For decades, the hard core left (perhaps a couple % or so of the population generally) denied and hid their socialist/communist inclinations for obvious reasons. Being a radical leftist was simply unacceptable to the general public, particularly in electoral politics. For good reasons of course but they knew to hide in the closet so to speak. Bernie Sanders is really the first major political candidate to publicly campaign successfully in a national election in American history. He was a legitimate threat to win the nomination but for the obvious conspiracy within the establishment of the national democrat party to prevent his campaign from actually winning. He came perilously close.