Actually, your second link doesn't say what you think it says. It says that people believe that Democrats believe that, not that Democrats believe that. Yes, it seems a weird thing to poll about.
Your fourth link is misleading. You've picked a link from a moment in time when Barr had released his summary of the Meuller report but Meuller's criticism of Barr's summary as being inaccurate had not been released.
The second link's poll includes a breakout of Democrats' beliefs in what Democrats believe, in addition to the overall figures. So 65% of Democrats agreed at the time that Democrats don't accept Trump as the legitimate president. I realize it's not the same exact question, but it is similar. There are also other polls that I didn't include that you can find with similar results.
As for the fourth link - I am not sure of the timing of that particular poll (I just pulled that from a search earlier), so I'll have to take your word on that. Thanks for pointing it out.
Your fourth link is misleading. You've picked a link from a moment in time when Barr had released his summary of the Meuller report but Meuller's criticism of Barr's summary as being inaccurate had not been released.