My reading of Nate Silver’s article suggests that the OC (original commenter’s) comment is right though. Quote from the article:

the movement could just be random variation in the polls — if Harris really is ahead nationally by 3 points and in the Blue Wall states by about 1 point we’d expect her to have better and worse weeks that vary around that average.

Sounds like phantom momentum to me. And Nate also agrees with the part about there being Republican bias in the polls,

First, are polls from Republican-aligned firms more favorable to Trump this cycle? Yes, … Harris is ahead by 3.0 points nationally in this simple average. But when you look at only Republican-aligned firms, she’s up by only 2.0 points. Removing those polls from the average brings Harris up to a 3.4 point national lead. These aren’t huge differences, but they’re not nothing. Combined with a similar pattern in state-level averages, polls from Republican-leaning firms could push polling averages — and by extension forecasts — rightward.

This last sentence is important so I’ll repeat it,

Combined with a similar pattern in state-level averages, polls from Republican-leaning firms could push polling averages — and by extension forecasts — rightward.

Of course Nate believes, as you state, that he’s able to account for it by adjusting for the house effects and such. Which would overcome the flood.

He then seems to go on and justify that his house effects are accurate by comparing with pollsters whose averages are excluding Republican polls (thus avoiding the bias completely) and saying that he winds up with the same result as them.

However, it’s really interesting to note that most of the polling averages he compares with don’t include as many GOP polls.

In fact it’s Nate’s own average that is the lowest in favor of Harris. In fact I think 538 is the only other one that does even include those GOP polls.

And somehow these are the ones that show the GOP candidate with a lead.

In fact, VoteHub - the one using only high quality nonpartisan polls - actually has Harris winning the Electoral College currently., 270 vs 268: https://polls.votehub.com/

Electoral College average
Harris 270, Trump 268
National Average
Harris +2.3
Tipping Point (MI)
Harris +0.1
Electoral College Bias
R +2.2

Now Nate can easily justify this as a tiny difference within the margin of error. And he’s be right, of course. But I feel that this shows, even after all the hard and brilliant work by Nate and folks, the flooding by the GOP polls seem to be off by just enough to push things over the edge. Ignore them for more accurate data, and the picture looks different.