(The counties in gray did not yet have Partisan Voting Indexes (PVIs).)
Here is my analysis of a state that has also been widely discussed by users with better knowledge than me.
After being firmly in the Republican column in the early 20th century and voting for Franklin Roosevelt the first two times, Wisconsin became the famously swingy state in 1940 and mostly remained that way since, leaning Republican from World War 2 to 1960.
In the 1970s, Wisconsin’s PVI became slightly Democratic. The northwestern counties were swingy or Democratic-leaning. The Fox Valley, from Green Bay to the Illinois border, mostly leaned Republican. Milwaukee and Dane County (Madison/University of Wisconsin) were of course Democratic strongholds, as were the counties along Lake Superior.
Wisconsin, like many states with farming as a significant part of their economies, became bluer in the 1980s with the farm crisis. Wisconsin’s shade of blue lightened in the 1990s enough that the state almost voted Republican in 2000 and 2004. The counties in the southwest became more Democratic while the other western counties mostly trended rightward.
Being from a neighboring state, Barack Obama (D) did well in Wisconsin as shown by the slightly more Democratic hues in 2008 and 2012. 2016 was kind of a reversion to the post-farm crisis norm, only with significantly redder rural areas and bluer city/college areas.
Here are the results in table format.
Here are the results in map format.