Wisconsin has been a swing state — where voters waver between electing Republicans and Democrats — since at least the mid-20th century, according to experts.
Republicans and Democrats began their intense competition in the state in the 1950s and 1960s, once the Democrats became a prominent force in presidential and gubernatorial elections. However, even in the late 1800s, there were close two-party races, according to University of Wisconsin-Milwaukee history professor Jonathan Kasparek.
In the 21st century, the state has become even more contested, with three presidential elections decided by less than a single percentage point—something unseen before 2000.
Experts believe one of the main factors that has been driving Wisconsin’s partisanship is the somewhat even division of the state’s population between small towns and cities, which have had opposing trends in partisanship towards the right and left — respectively — since the mid-20th century.
Wisconsin Public Radio: How long has Wisconsin been a swing state?
Google Books: Presidential Swing States