You don't see the Driftless Area standing out as a Democratic stronghold on a statewide election map before Russ Feingold's win in 1998. Compare Feingold's map (left) to Michael Dukaki's narrow win from ten years before:
At the presidential level, the area's history as a place of Democratic strength dates back about two decades. In
1976, it's an area of Democratic weakness within each of the four adjacent states. You don't even see a huge shift after the Farm Crisis. Clinton did well in the region, but won by no more than he did across
the entire rural Midwest. The
2000 election is the first in which it stands out, and by
2008 Obama won it by a wide margin, taking Wisconsin counties like Grant and Crawford by 25 point margins or more.
These counties swung against Obama by double digits in 2012, and after a second large swing in 2016, Trump was winning narrow majorities over Clinton.
You see the same pattern in downballot contests in all four states: Before 1998-2000, the region doesn't have a distinct or unified voting pattern, and if anything tends to favor Republicans in competitive statewide elections. And I remember a local Atlas poster (Gass, maybe?) mentioning that local elections in the Wisconsin part of the region continue to favor Republicans.
There are clearly a mix of factors at play. I'm a bit skeptical of answers that lean too heavily on settlement history as a cause. Here's something that seems to be true outside of the South and extremely sparsely populated rural areas in the West:
Marginal agricultural regions, especially those with rugged terrain, tend to be more friendly to Democrats than highly productive ones, at least at the federal level. You see this in northern New England and parts of Upstate New York. I think we often assume that these areas overlap with rural areas more oriented toward recreation, but there's a distinction between a place that attracts middle class tourists and wealthy retirees and one that attracts people who are just looking for relatively cheap but workable land. The people attracted to these areas, and those who remain in them, are not necessarily liberal or wealthy, but they do tend to be different from those whom you would find elsewhere.
