It's the first national poll that meets CNN's standards since early July to find that there is no clear leader in the Democratic nomination fight, and the first all year to find Biden even statistically insignificantly behind.
So does Monmouth's poll mark a turning point in the Democratic race for president? Or is this merely an outlier that later polls won't back up? My inclination is to say that it's an outlier and to pay attention to the average, though the truth is that we just don't know.
Let's place the Monmouth poll into context of what other polls have found.

If you average Monmouth's poll with the three other high-quality national polls taken this month from CNN/SSRS, Fox News and Quinnipiac University, you get a clear Biden lead: Biden at 28%, Warren 19% and Sanders 14%..
When you break it down further, you see that Monmouth did not poll at a vastly later date than others or among a different set of voters.
Monmouth conducted its poll on August 16-20 among voters who say they are Democrats and independents who say they lean toward the Democratic Party.
Interestingly enough, CNN did its own poll of the race August 15-18 among this same defined group. Unlike Monmouth, CNN put Biden up with 29% to Sanders' 15% and Warren's 14%.
The CNN poll looks a lot more like other polls of the race taken this month when it comes to Biden. Fox News was in the field from August 11-13 (within a week of the Monmouth and CNN polls) and showed Biden at 31%, Warren 20% and Sanders 10%. Unlike CNN and Monmouth, Fox didn't preassign voters to the Democratic primary based on party identification. Instead, they asked all voters which primary they'd vote in.