A head to head comparison of the South Dakota 2020 Primary gives us an idea of the break down of the voters.
Joe Biden got 78% (41k) of the vote to beat Bernie Sanders (12k votes) by 22%. There was no Presidential Primary for the Republican Party in the State of South Dakota, thus there are no results for President Trump at the Primary level.
In the Primary, Joe Biden won all 66 counties in the 3-way match up, with Bernie Sanders and Donald Trump winning nothing in South Dakota Primary. There was no Presidential Primary Elections for the Republican Party.
Bernie Sanders vs Joe Biden
In a head to head match up on just the total number of votes, Biden (78%) beats Sanders (22%).
These 10 counties play an important role in these primary elections. Winning a sizable minority in either of the top two counties they can capture a large number of votes.
Joe Biden won the most votes in the state of South Dakota. Bernie Sanders won fewer votes. Joe Biden won all counties, hence allowing him to win the primaries in South Dakota. There was no Presidential Primary for the Republican Party in the State of South Dakota, thus there are no results for President Trump at the Primary level
Related References: 2016 South Dakota General Election Story, 2016 South Dakota Primary Election Story