They are a joke. Steady stream of negative coverage, followed by poll asking people what they think based on that negative coverage, and surprise . . . poll numbers stink.
They are relying on the fact that a lot of people get their news from one source and/or don't get into the weeds when it comes to politics, so they don't really know exactly what's happening. That's why someone like Obama--an abject failure--could repeatedly make a speech patting himself on the back and his follows ate it up.
I wouldn't be surprised if Trump himself was leaking some of this stuff.
He puts it out there knowing the media will lap up anything negative about him and then another person who was in the room or part of the conversation simply comes out and denies the story being leaked, thereby discrediting the media even more.
With the cord cutting phenomenon and more people getting their news online from alternative sources, stuff like this matters less and less and can be turned around to hurt the mainstream media.
As far as poll numbers are concerned, the election proved how untrustworthy that can be.