Sorry I havent posted in here in a while, there was a good week or so without any solid poll updates and the main poll I do like to use (Economist/YouGov) has been rather erratic recently with 6 point swings for Biden and Warren on a weekly basis. Now that we've got a new batch we can dissect things a bit:
1 - Warren now regularly polling in the 20% range
Apart from one poll on 10/7 that has Warren at 15% (Which is almost certainly horse shit and I'm not even a big Warren fan) Warren now regularly is polling in the 20% range averaging 23% to 27%. RCP has her average at 23.4% but thats because the bs 15% poll is warping the numbers lower then what they are. With Biden polling back and forth between 25% and 31%, Warren's stronger polling places her within spitting distance of Biden at second place. Bernie meanwhile is lagging at a now distant third place, polling between 13% and 16% a full 10 points behind Warren now.
A quick glance at the overall trends show that when Harris bit off a lot of Biden's support following the first debate performance, those former Biden supporters have since gravitated towards Warren's camp rather then back to Biden. This is evidenced by Harris's decline since the debate (exactly 10.0% since July 4th) while Biden's numbers have been about the same since the same date (27% to 29%).... That 10% Harris lost that Biden never regained can clearly be seen being absorbed by Warren, who since July 4th has seen her numbers increase by almost that exact margin (+9.9% since July 4th).
2 - It's possible that Biden's remaining supporters are his core base that will be difficult for him to lose
The transition of the voter bloc that went from Biden to Harris following the first debate, and then from Harris to Warren ever since lends credence to a theory that those voters were wavering Biden supporters who were waiting to jump ship to a different candidate the first chance they got. Harris following her strong performance in the first debate, began to rival both Warren and Sanders in polling where all candidates were around 13% to 15%. With Harris not being as far to the left as Warren or Sanders though, Biden voters who were itching for another more moderate candidate to back switched from Biden to Harris and then migrated over to the Warren camp rather then back to Biden
This all entirely theoretical though. It's equally possible that there are still wavering Biden supporters who are willing to jump ship but just werent impressed with Kamala Harris following her performance in the first debate. Maybe they would back Buttigieg or Beto O'Rourke if they suddenly surged in the polls or had strong debate performances. It's worth noting though that even if this were the case, the distance between Biden and the rest of the more moderate candidates still in the race is oceanic in size..... Buttigieg and Harris are around 5% in support well outside of the top tier of candidates in the race, while others like Beto or even Andrew Yang poll closer to 3% and are in even worse shape. Booker, Klobuchar, Tulsi Gabbard, and Castro all struggle to get north of 1% in the same. This means that the chances of one of these more moderate candidates surging in polls by a large enough margin to make Biden supporters completely reconsider their support is almost impossible, indicating the remaining 25% or so that supports Biden will likely remain with him through the remainder of the race, or even grow once the lesser moderate/centrist candidates begin to drop out.