A head to head comparison of the Wisconsin 2020 Primary gives us an idea of the break down of the voters.
Donald Trump got 41% (617k) of the vote to beat Joe Bider (582k votes) by 39% and Bernie Sanders (294k votes) by 20%.
In the Primary, Donald Trump won 56 counties in the 3-way match up. Biden trailed behind Trump winning 16 counties with Sanders winning nothing in Wisconsin Primary.
These 10 counties play an important role in these primary elections. If a candidate can get a sizable majority or even a high minority in the biggest counties (Milwaukee, Dane, Waukesha) they can win a majority of total state votes.
Bernie Sanders vs Joe Biden
Joe Biden vs Donald Trump
Donald Trump vs Joe Biden
In a head to head match up on just the total number of votes, Joe Biden (67%) beats Bernie Sanders (33%). Donald Trump (51%) beats Joe Biden (49%). Donald Trump (68%) beats Bernie Sanders (32%).
Joe Biden won an advantage in the three largest counties (Milwaukee, Dane, Waukesha) over Donald Trump but not obtains enough votes in the other counties to beat him in the 2020 Primary election in the state of Wisconsin. Donald Trump achieved a majority vote in other populous counties, securing him the victory over his opponents.
Related References: 2016 Wisconsin General Election Story, 2016 Wisconsin Primary Election Story, 2012 Wisconsin Primary Election Story, Wisconsin Early Voting Absentee Data on Nov 1st, 2020 as compared to 2000 through 2020 General Election Votes