On September 18, just three weeks ago, the 538 polling average had Biden +6.7, roughly in the range it’s been all year. Today it’s Biden +10.2.

For comparison, here is the same site’s final polling average from Nov. 8, 2016. Actual results: Trump 46.1% and Clinton 48.2%. In other words, Clinton seemed to be +3.9 in the popular vote and carried it by 2.1, a difference of 1.8 points.

In my memory, some election models correctly forecast Obama's narrow win in 2012, encouraging belief that the science was all worked out and that Clinton +3.9 in 2016 was durable. It obviously wasn't, given polling errors and the realities of the Electoral College.

This year, Biden +10.2 is also subject to polling errors, the Electoral College, the pandemic, uncertainties of mail-in voting, and who knows what else the next 3 1/2 weeks. Still a candidate would rather be +10.2 on Oct. 9 than the reverse.