The entire baseline for his predictions, plus or minus some additional adjustments. Everything after that is rooted in the original poll-aggregate foundation.
Nate went further post-debate performance, knowing where Biden stands in a variety of polling and that this was the worst debate perhaps in the history of debates
He was not telling Biden to drop out the day before the debate. He was telling Biden to drop out the day after, but before he actually inserted "bad debate performance" into his model and rerun a thousand model elections. This is what always gets Nate in trouble. He shoots from the hip on hot-button issues, rather than remaining academic.
More importantly there will be no major positive event that overrides it.
Trump tanked two debates against Hillary and still squeaked through on election day. Nobody is going to be thinking about this debate by the time the Olympics are over.
Nobody can provide me a single data-point where Biden isn’t performing significantly worse than his 2020 race where he won by merely 40,000 votes across 3 battleground states.
2020 had some of the highest turnout in US history, thanks to mail-in voting and quarantine. 2024 is going to see a huge drop off in participation. It isn't immediately clear which candidate is going to suffer the worst from the deficit in support, as Biden has banked hard on appeasing moderate conservative voters while Trump trundles further and further out into right-wing.