Sourced from RCP. As you probably know, they don't weight the polls or assign pollsters grades like 538 does. This has some drawbacks, sure, but it's tidy and provides a basis of comparison for where that same aggregator was at this point in the race. I did a raw number dump into excel from polls between around or about May 2016 and 2020 and using today's date as a hard cutoff. I'm not going to do re-run the numbers for every single rust belt state as I never claimed Clinton was outperforming Biden in every single rust belt state, I was specific to WI and, further in my most recent post I acknowledged that 538's analysis is still super solid for two of the states I've had time to dig into (PA and FL).

My suspicion would be that Silver and Co. incorporate outliers into their predictions and remove the results of any individual polls which greatly fall outside of any established trends. This of course is all well and good if you're comparing 538s predictions to itself, that is, you'll get consistent and valid numbers which are useful. The same of course cannot be said for comparing 538 and RCP, one is literally just a list of polls and the other has some methodology baked into the cake. The last time I checked Ohio and Michigan, two states which I made no claims about in my prior posts, RCP had Clinton barely outperforming Biden at this same point in the race. At that point it was probably something like May to August, or May to late July. Biden has only polled stronger since then so I can only assume he's pulled ahead of Clinton's gap in that time.