The chart above reflects the results of the latest Monmouth University Poll -- done between June 12th and 17th of a national sample of 306 registered voters identifying as Democrats/Leaners, with a 5.6 point margin of error.
The chart above reflects the results of the latest Economist / YouGov Poll -- done between June 16th and 18th of a national sample of 506 Democrats/Leaners. The margin of error for the whole 1,500 adult sample was 2.7 points, so the moe for Democrats/Leaners would be in the 5 point range.
Both polls show Joe Biden hanging on to a significant (but not overwhelming) lead. But the interesting part of these polls is what has happened to second place. In both polls, Elizabeth Warren has taken a 1 point lead over Bernie Sanders.
That 1 point lead is within the margin of error, so it is not statically significant. It would be more accurate to say Warren and Sanders are in a virtual tie for second.
Still, it's cause for celebration by the Warren campaign and it's supporters, because it shows she is gaining support (while Sanders is losing some).
It'll be interesting to see if these charts look different after the Democratic debates next Wednesday and Thursday.