And this ain't ancient history. This is only 12 years ago. If you include Midterms, polls underestimated Democrats in 2022 and 2018 as well.
This isn't just a Trump effect either. In 2016, we had a big realignment on education and it was something pollsters weren't weighting on. In 2020, we had a large partisan non-response bias likely due to COVID.
There is some evidence this cycle the partisan non-response bias has flipped.
And that's not the only change from 2020. Most pollsters are now weighting on 2020 recall vote in an effort to adequately capture enough Trump voters.
So embrace the idea that polling error can go in both directions. In practically every election it does depending on the state.
This race is close enough in the 7 battlegrounds that which direction the polling error is in and its size will determine the winner. And all 7 are within a normal sized polling error. So sweeps for either candidate are quite possible.