If I already posted it apologies still jet lagged from trip to Philippines.
The polling leading up the debate had been bad for Biden all along but he insisted he wasn't dropping out. After the debate, Pelosi went to him and showed him internal polls that had Trump getting 400 electoral votes if Biden stayed in. He still wouldn't drop out because he had taken his performance at the debate as personal and wanted to redeem himself. Pelosi eventually convinced him to drop out by showing him effectively multiple lists of donors who were refusing to put in any more money until Biden dropped out.
At that point the plan was, Biden drops out, they have a open primary. Pelosi said she strongly believes Harris would have won the primary and it would have strengthened her campaign to do so since that was a sticking point all along, she was selected not voted.
The next problem was Biden finally agreed to step down, and then immediately endorsed Harris. He wasn't supposed to, it was essentially a stab in the back of Pelosi. The Dems discussed it and decided with the delays by Biden and then the endorsement they simply didn't have time to do that open primary.
Pelosi per the article is still furious wiht Biden, it doesn't mean she would have won POTUS if Biden had cooperated with the plan but the idea is their internal polling was 400 and he ended up 312, so in just a few months she cut into the polling by nearly 25%. If Biden had dropped out earlier, and done it per the plan, it MAY have helped. My guess is he still wins based on just the popular vote, but it sounds like despite all the praise for Biden being unselfish, the leadership actually is pissed off at him for NOT cooperating.