Dane County WI, home of University of Wisconsin Madison, was a Bernie Sanders stronghold in last Tuesday’s primary, Sanders prevailing 63% to 37% there over Hillary Clinton.

Exit poll data indicates that 15% of Sanders voters across the state did not vote for Democratic Supreme Court candidate JoAnne Kloppenburg, compared to 6% of Clinton voters who failed to do so.

As this downballot behavior seems a particular point of contention between Sanders and Clinton partisans, it’s instructive perhaps to drill down into Dane County results to see undervoting patterns for the Supreme Court contest.

There are 216 precincts listed in the Dane County results.

It’s a little tricky to define undervoting. Since this Supreme Court race was seen as a particularly partisan litmus test, all Democratic voters might be expected to be Kloppenburg voters. So for the purposes here, undervote is defined as the difference between the Democratic vote and the Kloppenburg vote, expressed as a percent. To cut to the chase, here is the precinct data using that definition:

So generally as Sanders support goes up, so does undervote, approaching 20%. So this is consistent, or even a bit higher, than the exit poll number of 15% for Sanders voters. Note that the downballot behavior of university students, or young voters, might be different from that of Sanders voters generally across the state.

This definition of undervote underestimates the actual undervote of Democrats, as some Republican voters may have voted for Kloppenburg, either randomly or perhaps because they agree that her opponent Rebecca Bradley is a hateful nitwit. Indeed, it can be seen in the precincts where Sanders support was weaker, the “undervote” is actually negative, indicating Republican crossover votes.

These results are consistent with election data from Milwaukee County, looking at those Milwaukee wards that had high Sanders support. These wards are associated with UW-Milwaukee and Marquette University.

For the top ten Sanders wards in Milwaukee:

WARD DEM BALLOTS SANDERS% KLOPPENBURG UNDERVOTE 130 692 88% 348 50% 137 460 86% 348 24% 136 667 83% 481 28% 138 1557 83% 1253 20% 128 840 83% 219 25% 134 523 80% 387 26% 133 553 79% 433 22% 191 255 77% 151 41% 135 612 76% 471 23% 242 537 76% 460 14%

So the undervote rate there is particularly high.

As for the quoted 15% exit poll figure?

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note: To ensure reasonable statistics, only those precincts with more than 100 voters are plotted. Also, for Dane County there was one precinct, T Vermont Ward 1, that was an outlier and omitted. It had 219 votes for Sanders and only 2 for Clinton, and had 321 votes for Kloppenburg, indicating that most of the 163 Republican ballot voters in that ward went for Kloppenburg. Weird. Could be a bogus result.