These charts reflect the results of the CNN / SSRS Poll -- the latest being done between October 17th and 20th of a national sample of 424 Democrats and Leaners, with a 5.8 point margin of error.
This is a very small sample for a national result, but it is a respected poll. It shows that Joe Biden has rebounded and currently enjoys a large lead over his opponents -- 15 points over Elizabeth Warren and 18 points over Bernie Sanders.
The second chart shows the support for those three candidates in this poll over the last year.
NOTE -- Candidates were only included if they registered at least 2% support.