Sean Trende of Real Clear Politics highlights a key problem for presidential election polling.

In 2016, as I was preparing to write my “Why Hillary Will Win” piece, I decided to have my able then-assistant, David Byler (now of Washington Post fame), do a bit of research. His job was to look up the share of the electorate that pollsters were anticipating for whites without college degrees and for African Americans.

What he found put an end to the piece. It seemed a big bet was being placed on 2012 levels of black turnout occurring in 2016 and, more importantly, that pollsters were badly underestimating turnout for whites without college degrees. In previous years, that hadn’t really mattered – whites with and without college degrees voted Republican at roughly the same levels. Underestimating the share of whites without college degrees and overestimating whites with college degrees wouldn’t have mattered in 2012 or 2008, because their votes were fungible.

On a hunch, I went back and looked at the poll errors for 2013-15, and it became apparent that the errors for 2016 followed much the same pattern: They were concentrated in areas with large numbers of whites without college degrees. Indeed, the size of the poll error correlated heavily with whites-without-college-degree share (p<.001); you could explain about one-third of the difference in the size of poll miss just from knowing the share of the electorate that was whites without a college degree.

We all know what happened next. Trump surprised observers by winning states that Republican presidential candidates hadn’t carried since Debbie Gibson and Tiffany fought it out for top placement in the Top 40 charts. The misses were particularly pronounced in the Midwest.

Most pollsters attributed the misses to the failure to weight by education, and when one brings up the errors from 2016 with respect to the 2020 election, the answer typically is “pollsters now weight by education, so they’ve fixed it.”

But have they?