This is the fifth national poll in about the last week that has Biden in the range of between +18 to +20 over Sanders. (RCP doesn’t yet have this new Monmouth poll up as of this moment.)
While “asymptoting” isn’t the right word, it seems that Biden really does currently have about an 18 to 19-point lead over his next closest competitor. (Point being that the fairly recent Emerson poll with Biden at +8 and the fairly recent The Hill/HarrisX poll with Biden at +32 are outliers.)
From Monmouth:
Former Vice President Joe Biden maintains his front-runner status among Democratic voters nationwide, but some female candidates – namely Massachusetts Sen. Elizabeth Warren, California Sen. Kamala Harris, and Minnesota Sen. Amy Klobuchar – have seen some small but notable upticks in their favorability ratings over the past month. The latest Monmouth University Poll also finds a drop in support for Vermont Sen. Bernie Sanders and a decline in the net rating for former Texas Rep. Beto O’Rourke.