From U.S. News, a counter-poll to Monmouth's:
"Emerson College ... released a new poll Tuesday [rated "B+" by 538] that finds Biden with a 7-point lead over Sanders, 31%-24%. Warren garners 15% and Harris rounds out the top four with 10%. All other candidates polled at 4% or less….The Emerson poll was conducted between Aug. 24 to 26 and surveyed 627 Democratic primary voters. The margin of error was 3.9 percentage points.
"Emerson's survey polled head-to-head matchups against President Donald Trump, finding that Biden and Sanders are the only two candidates to defeat him. The poll found Biden leading Trump, 54%-46%, and Sanders defeating Trump 52%-48%. Both Warren and Harris tie Trump" ...
… so assuming the Emerson poll is reasonably accurate, the spreads between Sanders, Warren and Harris vs. Trump, either too narrow or nonexistent, lead to the inescapable conclusion that the spreads are far too perilous.
And so it goes.